I'm impressed you got everything done in 48 hours when making that many levels! Increasing jump height when you get smaller is a welcome addition too.
Somehow I got the game crashing at level 3 when I tried increasing in size in order to break the blocks. (or I assume that's what I'm supposed to do) Later I'll give it another attempt to see if I can get past it. As a suggestion I agree with another commenter that the "head-bump" jumps can be annoying, but I did get the hang of them in the end. Adding a more clear distinction between normal air and a death zone would be another suggestion.