It's pretty impressive that you managed to make a game with so many levels in such a short time period, but i definitely feel like you should have spent more time on polishing you character controller and enemies than on making levels. The fact that the enemies and spikes' hitboxes don't match with their sprites at all is probably the part of the game that caused me the most frustration, and there are definitely very easy fixes for making the character controller feel better, since as of now it feels very floaty and like i have very little control over them, which is kind of a problem in a precision platformer,  i highly recommend watching this video from Jonas Tyroller the next time you make a 2D platformer. I really liked the game's graphics and audio

I'm trying to click Start but it doesn't do anything, is the web build broken?

Really like this! Tight platforming gameplay and nice simple retro visuals. Only suggestion from me would be that the triangle enemy colliders are a little unforgiving! Maybe that's just me. Good job!