How can I calibrate my IPod touch screen?

On the top of the screen there's something of a black line where the screen should just be further up. It seems to be only on YouTube and safari and that's it, none of my other apps. Its really bothering me and I don't know what to do because everybody says you have to bring it to the store but i don't want to tell my mother I broke my iPod again. soo if anyone can tell me why it's doing this or If there was any way I could fix it, it would be greatly appreciated!