You got one computer in your room? Pffttt.... Come back when you got 7.
But on a more serious not. Yea congrats. I guess I was lucky. I first bought my own computer when I was 13. And it was in my room. But before that. Yeah, The stupid cover up window to hide your real activities.

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Just don't spend too much time on it. Not to alarm your parents that you are spending too much time on your computer instead of homework.
Guess I'm lucky for my parents not to snoop into my things on my computer. May be when I was younger. But now my knowledge of computers completely surpasses them. They can't really get into my things, then again I'm 18 and they said they would respect my privacy. I'm old enough not to do anything stupid.
So maybe try to brush up on your computer skills. But don't go into super PARANOIA mode and add a password at every possible point. Just don't look too suspeicous.
Also, when you leave your computer for a short moment. Use Win Key + L. IT basically locks the computer. So you need to 'log in' again, but all your web pages programs are still loaded in the background. This was for me mainly to stop My friends and brothers touching my computer. I hate it when they touch it, X(, Even on my 'Clean' computers.