I remember watching this movie a couple times on TV, perhaps it was an after school special in the 1980s? The basic gist is that there is a girl who simultaneously tries to be herself and have girl friends and do girly things, but also poses as a boy and has boy friends who do boy things. Obviously, she keeps both identities secret … until the end when it all implodes.
One scene I remember clearly is when she paints her bike red so that she can fit in with the other boys
The final scene of the movie, there is a performance and the girl has to perform with both her boy and girl groups of friends. She wears a dress and performs with first with girls. Then, she changes quickly and puts on her cool boy clothes over her dress, and plays piano/keyboard with her boy friends in their band. But as they perform, her dress starts to become untucked and slips out, and everyone realizes that she is in fact a girl.