"I wish I didn't have to take Zoe and her friends to the mall," he said, forgetting that he was holding the stone.
When it glowed, he had an urge to close his eyes. And when he opened them, he panicked. What did that wish do?
Zoe entered the room. "Didn't you hear the honk?" She asked. "It's your ride to work," she said.
The reason he had to drive Zoe and her friends to the mall was because his mother had to go to work. The wish had made it so HE had to go to work.
He hoped that was the limit to the misspoken wish. That he had to sub for his mother that day.