Once I complete all of the levels (the 3) then go to the 3rd level, & do the b side (or whatever it says for the next set of music) I complete it, then go to do set C, and it says to record and make a beat. I click on one of the instruments, make the music, then press the back button, but it disappears, causing me to be stuck on that screen, unable to play or mess around with any other instruments. Overall, it's a great game, & since I'm in band (I play an instrument, but not the flute, which was one of the instruments in the second level) the game is extremely fun for me, since I enjoy band a lot. The game also makes me wish I did drums 😄. The problem with the back button disappearing happens when I go to do one of the guitars, the lowest one I think, so I don't know if that happens with all of the instruments or just that one specifically.
edit: if the maker of the game sees this, or if anyone else has this problem, I would personally also say it, because it might not be just me having this problem.