This is quite clearly one of your first games, but i'm glad you finished.
This game isn't a masterpiece, it didn't keep me immersed, but i'm glad that it exists solely because of the experience it gave you. You will learn so much from this experience, and hopefully you keep going and make better games. As a 12 year old myself, i'm always trying to learn, and I have some criticism to hopefully help you learn in the future.
1) The Controls need work. The newgrounds page scrolls when the arrow keys are pressed, but in the game itself, there is nothing to help the player out. Coyote time, which will allow you to jump shortly after leaving a platform, can be implemented in construct by simulating jump if you press the up arrow about 0.2 seconds after leaving a platform. The jump is also waaaay too high, and the platforming isn't engaging because of that.
2) The camera, as mentioned by @youthfulidealism, is not lerped, making it feel choppy and stiff.
3) No audio present. There are several great programs, such as sfxr, or chiptone. (https://sfbgames.itch.io/chiptone)
4) The graphics could use some work. Try devoting a bit more time to making them, but you don't actually have to make much art. You could have used a cube, which honestly would have looked better. Try to add squash and stretch, by making separate objects for the player graphics, and the player collision, and pin them together. Then, on certain calls, change the player graphics width and height accordingly.
But overall, even though this isn't the best game, i'm happy you were able to upload it, and finish on time. Great work.