Really impressive work for 48 hours!
Great theme integration, I really like the idea of a scaling character in a platformer, and there's a good number of levels exploring that concept. The branching paths and hidden collectables are a really nice touch too.
The web version seems to lag a bit when a new particle is emitted, you mentioned in the description that you're still new to Godot, so just for the future Godot currently doesn't automatically cache particles in web games which is causing the lag spikes. To fix this, you need to create your own system, and for game jams that can be as simple as an off screen node that holds a copy of all your particle emitters which are set to fire at the start of the game. It's not the best system, I wouldn't use it for any larger games, but it works great for something made over a weekend and keeps the in-game lag spikes to a minimum.