Quite a fun (but tricky) little game. I can see the idea is to "build" to "scale" over obstacles, although I do wonder if there's a creative way to play with the concepts of large and small within this game as well.
My main suggestion would be to add different types of difficulty to the game and reduce the parts of the difficulty that can feel artificial. For instance, if the blocks you placed were made larger, the timing window to jump on them wouldn't be as tight, and a single block would be able to turn a jump from being impossible to being easy (instead of being barely possible). This would leave room for more of the other types of difficulty, such as puzzling out how to beat a level or having to multitask to deal with multiple threats at the same time.