It did work

Jon closed his eyes for a moment. When he opened them, everything looked the same, except that Emily was starting to hesitate. "Jon... what am I doing? I wanted to..." "It's okay, Emily," he said. "I reversed it. You don't want a dick any more." "But you can't reverse wishes." "I wish I knew how that happened... oh, I get it. It reinterpreted the other wish. You're still happy as you are... which means happy as a person who once had a one hour transformation spell on her." "But that isn't an 'are', that's a 'were'." "Every 'were' is also an 'are'. If you were a person with something, you are a 'person who once had something'." "I think I'd better get some underwear," said Emily. She was still dressed as a schoolgirl with no panties.