This game is very clever, I loved the style of the 2D world and having the 3D world alongside it is ambitious, but you definitely pulled it off. To improve, the ball is very fiddly to get on the buttons so maybe consider making that easier. The player also teleports around a lot when changing dimensions, which confused me at first because it felt like the level was restarting and I didn't realise it was the same world.
All in all, this is a great game. Well done!