Braceface (2001)

In an effort to prove she's not such a ""girly-girl"" Sharon decides to form an all girl rock group for a battle of the bands contest sponsored by a ‘girls' magazine. Dion, thrilled at the opportunity to design their outfits, jumps on board, but when Mangled Metal hears about the gender limitations they are outraged. As a result, they decide to disguise themselves as females so they can enter the contest as well--and win the expensive music equipment. So as the girls take a walk on the masculine side (I'm not sure that joining a rock group is necessarily a masculine thing to do), the guys dress like Britney Spears wannabes and call themselves the Mangled Petals. Hilarity ensues when everything comes out in the open at the concert – literally.