Covered in Frills

"... a prom dress," Sandra finishes.
I saw a tiny spark from the stone and gasped as the tutu exploded into a big frilly petticoat. It dropped down to near the floor. The next thing I knew, a satiny dress poured out of nowhere, reaching up over where the leotard was. The neckline drops a bit, and the stitching changes. I stood there in a poofy pink prom dress while Sandra gaped in amazement.
"Oh my god," she said. She looked back at the stone in her hand. "This is too much! I wish the dress would turn back." She looked at me expectantly, then at the stone.
"What's wrong with it?" she asked.
"It can't undo wishes," I said, "You can only change the wish you made, or alter it's meaning."
She looked down at the stone, then back up at me, her mouth hanging open.
"Sandra?" said one of the cheerleaders outside the door, "May we please come in?"
She turned and opened the door, looking at the expectant cheerleaders with a look of total bewilderment. She probably didn't expect her fantasy to so literally become true.
"Um, look," she started to say. She looked back at me as if to ask for help. I stepped up carefully, daintily even.
"Everything will be fine if you come back tomorrow," I said. Sandra nodded and turned to the rest of the squad.
"Yes, tomorrow. We'll see you all tomorrow." The cheerleaders looked disappointed, but obediantly turned to leave. Once Sandra heard the door slam she turned to me with anger in her eyes.
"What the hell is going on?"
"My name was Jon, but a careless wish made me a cheerleader, and then I met you and I really liked you, but I think when we were having sex you came in contact with the stone that I tried to hide in my bra. Now you can have sex with any cheerleader at school and we're all submissive to you." I couldn't believe I'd just said all that! Sandra looked at me and shook her head.
"This is crazy! It's impossible! There's no such thing as a wishing stone!"
I stayed silent.
After staring off into space for a moment, she turned back to me.
"Lift up your skirt," she said. I did, petticoats and all, until whatever underwear I had on was visible.
"Do you like being a girl?" she asked me. I couldn't lie to her.
"It's different, a little strange... but yes, I like it." I said.
"What about wearing girly things? Like that dress? The cheerleading outfit?"
"Kind of," I said. It did feel strangely nice.
She seemed to think for a minute, then looked down at the stone.
"I wish..."