Good job for a beginner game!
Here's some tips :
- make it so when the user stop inputting a direction he stays in the last direction to be able to shoot left even when stopped
- make the hitbox of the player smaller in the vertical axis to pass more easily the small gaps
- make the player fall more slowly, the gravity is increasing to fast making precise platforming harder (there is tons of resources explaining on how to make a good platformer jump!)