It is an interesting idea, now I like the piano sounds as you change shape, that is very relaxing, and your drawings are clean and tidy :)
There is no level progression. Remember we play your game for the first time, you've got used to your game for 48 hours now. Make level 1 a simple one-platform with a gap - It helps new players learn to use the triangle. Then level 2, a tall wall to learn how to climb with the square, and so on.
What I don't like so much is the controls, it is difficult as you said. You cannot move the ball while it bounces, or the triangle while it flies, you can only affect direction that moment you shape-shift, and that give us players a very small amount of time to react. That makes it hard.
If the circle can be pushed left/right while bouncing, it will help. The triangle moves really fast, it has to slow down, it is hard to react when you near those spikes - is the triangle meant to be this fast? Do you use frame-limiting?
You spent your time unwisely with the menus. You should make a working demo that controls well, first. Leave menu's until last, you can always add menus in a post-comp version. Even a one-screen "hit any key to start" screen works.
I hope this is useful advice, I really think you have a nice game here, and you should work on a post-comp version :)