There are big collision bugs in the game, sometimes you can even stop being able to jump if you collide wrong (the game probably thinks you're still falling). Another problem that I find is that you didn't really use the graphics fully, they feel slapped on. You don't use the idle animation for your character and the enemies are barely visible against the background.

Game design wise I don't want to be too critical seeing it's your second game so I'll just tell you that there is no need for most games including this one to have such a long and floaty jump nor a double jump. You can configure it in a way that will feel quick and satisfying and then be able to level design around it. I don't know how that works in unity, but do tweak the physics around at the start of your project until it feels most satisfying to control