Help, I'm a Boy! (2002) on Netflix

Plot summary

Freddie, about twelve, comes across the book of spells belonging to an aged wizard who is looking for someone to take over from him. He reads some lines aloud to his friend Emma, and she repeats them, adding her annoyance about Mickey, a boy who often treats her badly. When the next morning comes, Mickey is in Emma's body and Emma is in Mickey's body. The wizard finds the book, takes it away and vanishes, leaving Freddie with no way to undo the spell, which turns permanent after fifty-four hours. Freddie, Emma and Mickey now have to work together to find a way back before the time runs out.