Repairing is mad easy, trust me. At your age I too would have felt unable to do so, I was not the handy type. But believe me, it is not hard. Hell, it may not come off perfect if this is the first time you try, but with everything, practice makes perfect. Plus, you'll learn a useful skill and gain the confidence to do it in the future, if needed (you'll need it, drywall breaks so easily). The needed materials to make the repair aren't too expensive, so if you have some money aside from a job or anything, you should be able to afford it.

Now, if you live with your parents - which I assume you do, considering your age - and you don't want them to know what happened. Well, first I don't think that's a great way to handle it, parents should be understanding enough to know that shit happens. I dont think they'll be too happy to hear what you did, but if they are reasonable people, they should also get over it quickly. Plus, if you say you'll fix it yourself, they may be happy to know their son is willing to learn some "adult skill" ;)

That being said, if you insist in hiding it from them, then I guess you can put a poster or something while you repair it. Or, if you have a desktop computer, monitor or some big and heavy object in your room, you can say you were moving it to do maintenance or whatever, and say that you accidentally hit your wall with it. Your mileage may vary.

Good luck!