Revealing mistake: After Josie kisses Allen M. at the concert, she moves back to her microphone to sing. Her Guitar part starts up again before she has her guitar pick out of the strings.
Revealing mistake: In the scene where the girls are looking at the Billboard paper Josie throws it aside but it doesn't move like a paper should. It seems to be made of cardboard.
Revealing mistake: When Josie is playing "Pretend To Be Nice" in the studio, she plays the first two chords backwards. It looks like it should be right, but any guitar player would notice it.