I'm about a week and a half late it appears but hopefully you still need some help.
I think you should sit down with your mother and help her understand where you're coming from. When you have a little time off, maybe a weekend, go back home to see her for a -visit-, yes, call it a visit, try and stay for a day. Talk to her about classes, let her know how great everything is going, tell her about something funny you heard, or an interesting fact. When you believe she's all buttered up, turn off any sort of distraction and kindly ask her to let you talk about something that's been bugging you.
At that point, slowly introduce the source of your issue; you enjoy your privacy, living on campus isn't going to be a good thing for you and you don't particularly enjoy it. If you've been doing it for at least a few months then she can't possibly say 'give it more time' so I hope you've waited a little while before thinking of trying this. Tell her that for her sake you had tried to put up with it to give her a little peace of mind, and that you hope to move back in. However, make it clear that you are not a recluse; you are capable of being social with others, but only for so long. If you want to help remedy her concerns, leave your room more, call her more often, heck call any of your family. Don't sit in your room all day on the computer, because it sounds like things like that put you in this situation.
Most of all, be kind about it. As frustrating as it is, she just wants to make sure you aren't like your cousins who don't get out into the world and socialize. Make sure she understands this, and good luck.
