This is a great showing for a first platformer! The art and music are really fun, pretty much every action has a sound attached to it for feedback, and I enjoyed trying to get the optional pages!
If you continue to work on this game or make another platformer, I would look into learning how to add both coyote time, and jump input buffering. They're small additions once you learn how to do them, but improve the feel of platformers immensely. Coyote time lets the player still jump for a small amount of time after running off a ledge. Jump input buffering lets the player input jump just a little early, and it will still go off if they hit the ground within a small amount of time after the press. You've got some tough jumps like this one in the screenshot below. Since there's no coyote time I have to jump early, but the platform above is low enough if you jump too early you bonk the robots head. Adding these features makes this jump WAY more manageable, and players will have a better time with your game.
Awesome work!