That's because it's chromatic; the smart thing would have been to let you pick a scale (a subset of the 12 notes that sound good together, and which are standardized)and then constrain your note input to that, using the inaccuracies in your drawing for expression.

Also, in-app purchases for individual sounds, no MIDI, and no audiobus? Sorry, total fail. No musician is going to buy this and no non-musician is going to be any better off with it.

Nsxwolf, I suggest a copy of Animoog (if you feel spendy) or Borderlands Granular (if not), either of which will allow you to enjoy a rich musical experience within certain limits by applying touch to other things besides chromatic sample playback.