Jon knew that Karyn was going to be at the mall, so he wished to be there and he was there. Unfortunately, he appeared in front of several witnesses. And scared the heck out of a couple of kids.
"Sorry, sorry." I have to really watch what I wish for, he thought.
He ran away from the crowd and searched for Karyn. He decided to wait until he really needed to use the stone, instead of just wishing for anything. Even the smallest of wishes (and with the best of intentions) could drasticly change things. And sometmes for the worse.
Jon had to be careful.