Factual error: There is no way Josie could have heard Alan M at the concert. First of all, she has a headphone in her ear, so she can hear herself sing, and second, the crowd is so loud, it's hard to hear people in the front row, never mind several rows back where Alan M was bodysurfing.
Factual error: In the final scene where the band are playing, the stage contains several amps, yet none of them are wired up to any instruments.