Very nice game, the fact you made everything is very cool, congrats.
The idea of the square get smaller is good and add a good variety of mechanics, but I think you can make it clearer, because I only noticed this is helpful after I read your reply here.
And, at least for me, its is better to jump using W, maybe add this button for jump and the player can choose which one is better for him? Just a suggestion. In general, I liked everything in the game.