Nice game, let's start from the things that I enjoyed the most: first and foremost, the level design. You got pretty creative and managed to always keep the game interesting, which is not an easy thing to do! Then the mechanic of changing size to fit through gaps is pretty cool (and also makes level look cool) and the music was amazing!
Now, here's instead a list of some small things that I would change to improve the game:
- explaining keybinds in game: even though the controls are listed in the itch page, it would be nice to have them in game so I don't have to tab out
- can't see when jumping while being very tiny: to solve this problem I would either reduce the jump height when you're being small or zoom out the camera while jumping
- distracting background: a pretty niche thing tbh, but for the background you probably want to use more dark/desaturated colors, and use vibrant colors only for the level layout. I suggest this article about Celeste Tilesets, it was an eye opener for me: https://aran.ink/posts/celeste-tilesets
Overall absolutely solid game, keep making games dude!