Oooh, interesting take on this set of mechanics! Having the level design center on changing size mid-jump is really cool. That being said, a lot of it ended up being really finicky, and a lot of the opening level design only really made use of the small and medium sizes as progression gates. Some coyote time (or more if it's already present - I couldn't tell) and some more ways to play with the size gimmick would be nice - what about trampolines that scale bouncing force with how big you are as you land on them, or boxes that you need to be big to push into position?
Great work!