What a cool little game! I loved the added extra of the hidden paths and pickups. I got frustrated on the last level though, the 1 gap jumps (Only one 1 hight corridors where you have to jump) seem a bit too punishing. Also I was struggling a bit with the fact that you can only scale up of you have enough space width wise, e.g. when you are standing next to a wall on your right you can't scale up, I feel like the game should just check if there is enough space in the other direction and then push you accordingly.
A small note, you should look into setting your rendering to nearest, to avoid getting blurry pixels (on the platforms it is very visible)
Enough complaining though, I think you made a really cool platformer with a cool mechanic! I really enjoyed it! Well done!