You know what happens when you assume

"Ok, we're in my room. Now what's this big secret you have to show me?" Sarah asked, impatiently.
"This", George said as he pulled the note from his pocket and handed it to her. She read it, looked up at him, and said "What book is this from? I don't think I've read it".
"No book. It's real", he said as he reached into his pocket and pulled the box out of his other pocket. He opened it to show her and she reached out to take it. Before she could touch it he snapped it shut.
"Careful, you can't just touch this thing carelessly. Who knows who you could turn into with all those clothes you have in your hand."
"You don't believe in this, do you?" She asked, a little curious herself.
"I don't know, but I'm going to find out right now", he responded, reaching into the bag and pulling out the football jersey.
"Now I get it. I was wondering why you were buying something that wouldn't fit you. But why a football jersey? You could have just bought a plain t-shirt."
"I wanted it to be noticeable. From my estimate, this will make me a few inches taller and about 100 pounds lighter", he looked over at her to see some interest. "Yes!" he thought to himself, "if this works, I could finally be with her"
"Here goes nothing" George said, holding the medallion in one hand and the jersey in another.
"I'll say", Sarah laughed after 30 seconds passed with no results. "Oh well, it was worth a try. No how about that fashion show I promised?" George could see the interest in her eyes fade as she turned to go change. He was about to ask her to wait when he felt a strong tingle all over his body.
"Something's happening!" he shouted, "Look!" as he held his hand out, they could both see it was getting thinner. His sausage fingers were soon slender, almost feminine looking. He felt his stomach shrink, his legs were getting thinner, everything about him felt thinner. He stood up so he could watch the world get smaller as he grew the expected couple inches but was shocked when he saw the top of Sarah's head coming up instead of down. Something was wrong but he didn't want to show any fear in front of Sarah so he just held on to the jersey and medallion as the changes continued. The tingling became burning and he soon fell to his knees in pain. Even his eyes were burning, he was forced to shut them as the changes came to an end.
When his head cleared, he opened his eyes and saw he was looking at the floor. He also noticed that he now had long blonde hair that brushed the floor in his current position on his hands and knees. Right away, he knew something had gone very wrong. He heard Sarah's voice to his right calling his name.
"George! George, answer me. Are you ok?"
"Ugh, I don't know. I'm still sore but..." he stopped when he heard the voice that spoke his words. It was clearly a girl's voice.
"What happened to me?" He asked in his new voice. Just then he felt a hand grab his arm, a very large hand from the feel of it. It was able to encircle his whole upper arm with no trouble. Worried about who this large man might be, he jumped to his feet and turned to face him. As he spun around, the hand let him go and he stumbled and fell right into his helper's chest. He soon realized this was no man but wondered who this woman was. After he regained his balance he brushed his now long hair from eyes and, looking up saw Sarah's face looking down at him. He looked down at her feet to see what she was standing on but saw her barefeet flat on the floor. Looking straight ahead he was now eye level with the bottom of her neck.
"H-How small am I?" He asked in a weak voice. Sarah ran over to her dresser, grabbed a tape measure she used for tailoring her clothes, and held it next to him. He knew it wasn't going to be good. For one thing, Sarah was only five feet even, and secondly, she was able to hold the tape measure at his feet with one hand and his head with another with barely any stretching.
"You're 4 feet, 4 inches tall" She said with a slightly amused tone.
"Wh-what?! That's impossible! This was a brand new shirt, it should have made me into a more in shape version of myself, not a little girl!"
"Oh, you're definitely an adult. Look", Sarah smirked as she turned him to face a mirror.
Afraid to look but knowing he had no choice, he was stuck like this for at least 12 hours he opened his eyes and looked.
Standing in front of him was quite possibly the most beautiful woman he had ever seen. She had shoulder length blonde hair, bright blue eyes, large but no grossly so breasts, and a perfectly shaped body. Looking down he saw that she was also neatly trimmed down there. He stared for a few minutes, taking it all in when it dawned on him that this was now him. He had full access to this body for the next 12 hours, he could explore every inch of it and it was all his! Suddenly this didn't seem so bad as he caressed his new breasts and played with the perfect nipples at the end. His hand started to drift downward when he heard, above him "Ahem! Get a room, short stuff"
Sarah was standing over him looking down. Looking in the mirror he was reminded of how small he had become and suddenly felt very helpless and naked (which he was, his old clothes having fallen off almost immediately).
"Do you have anything I can wear?" he asked Sarah.
She thought for a moment and went into her closet. After rummaging for a moment she same back with a bag and dropped in front of George.
"Try these, I haven't worn these in years. They might fit".
He knelt down and rummaged through the bag, it was mostly dresses and skirts, which he had no interest in wearing but there was a pair of overalls that didn't look too bad aside from the pink kitten on them. He also found a white short sleeve shirt with frills on the end of the sleeves.
The shirt fit but was very tight, it was obviously made for someone without his now impressive rack. The overalls were fine, but a little long.
"I can hem these" Sarah said as George took them off and handed them to her, "It'll only take a minute, just put this on for now" she said handing him an oversized (to him) t-shirt that went down to his knees.
While she worked on them, George walked around, taking in his surroundings at his new size. It felt like he was in a funhouse with oversized novelty furniture. The only problem was after a while the weight from his breasts were starting to bug him. He jumped up on the bed and held them in his hand. Each breast filled his tiny hands. No impressive feat there, his hands were now so small and dainty.
Sarah came over and handed him the overalls. "We're going to have to get you a bra for those monsters if you plan on staying like that for any length of time. And some panties. Sorry, but I didn't keep my underwear from my childhood. Besides, I doubt they'd even fit you."
"No way", George replied as he slipped the overalls on. He didn't want to wear the shirt since it strongly emphasized his chest but it also gave some degree of support so he put it on. Surprisingly, tight clothes on this body didn't feel the same as his old body. He didn't feel sloppy and gross, he felt almost comfortable, "We're going to stay here until 12 hours pass and I'm changing back", even he didn't sound too convinced as he said it.
"Come on", Sarah said, "It'll be fun. We can have a girl's day out. My treat."
"I don't know", George paused, "what if anyone sees me like this?"
"So? They won't even know who you are. Come on, let's go" She grabbed his hand and forced him to his feet. He tried to resist but he realized to his dismay that she was far to strong for him and he was yanked by his arm into a standing position.
"Ow! Be careful, you big oaf!" He joked, feeling his apprehension melt away. "watch the ogre grip there, Shrek" he teased her, remembering when she would call him that when he would do the same to her.
"Watch it there, little lady. You're not toe big for me take you over my knee, you know" Sarah said with a teasing smirk. And he noticed another look in her eyes, similar to the interest she had when she thought he would become a jock, only much more obvious. She was clearly excited by this.
"Fine, you win. Let's go. But I need some shoes, I can't go barefoot." George admitted.
"I can't help you there, hmm... I know" Sarah replied going back to her closet and returning with an old pair of white Keds.
"Try these on", she said handing them to him.
He dropped them on the floor and stepped into them. His toes didn't reach the end and they were very loose but they would do until he could get a proper pair. "Good enough" he told her and they both walked outside arm in arm.