The maximum length of a song in BPM's Song mode is currently 200 bars. To create a longer song, use BPM's Live mode. Instead of placing the scenes in a timeline in BPM as you do in Song mode, in Live mode you can sequence their order in your host by inserting the appropriate MIDI notes (chromatically, beginning on C1: Scene 1 = C1, Scene 2 = C#1, etc.).