This is a great submission for a first game! (and even more if you are also learning to code with this).
I think you should focus on fix some inconsistencies (like some coins that cannot be picked up, the enemy of the first level or the platforms without collisions of the second level).
Then you should focus on the fun part of your game: since it's a platformer, you probably want some challenge with nice rewards (look for some Mario levels as inspiration, however you're not using a scrolling camera for your levels and I can't remember right now any nice example with static camera). There is a lot of great content about game design on YouTube, you should check the GMTK channel for example.
But again: this is a great first step, keep going!