Six years ago, I felt similar to you coming out of high school. I had been programming for a long time, picking up whatever interested me. I was going to UCSD for Computer Science, and I already knew so much. There are a few points I'd like you to consider, though.
I didn't really know what to expect other than, "UCSD's CS program is ranked 6th in the nation." So I considered it an opportunity to learn even more, not just to prove what I already know. I looked forward to a fresh start in a new area, learning from people who obviously were very intelligent.
When I first took mandatory introductory classes, I thought, "This is so easy, I've been doing this forever." In high school though, few shared my interests at all. Here, I could make a study group and tutor others, and as some saying goes, "You can learn more by teaching."
When I finally got to upper-division classes, I saw yet another opportunity for growth. I knew what I wanted to focus on, but I also knew that I was smart enough to pick up something I was interested in without taking a class, if I put my mind to it. So I branched out, chose some classes that sounded interesting, even if they weren't directly related to my path. Machine vision, computer architecture, etc. Each one ended up teaching me new ways of looking at problems that I would never have considered if I hadn't taken that class.
University also provided me opportunities to branch out in another important area, social interaction. I joined the Ultimate Frisbee team, giving me a physical activity, new friends, and access to parties, things I never even tried in high school. I joined the student council (as the web designer) and gained insight into how bureaucracy worked.
My advice to you is this. Treat everything as an opportunity, perhaps a challenge to do something difficult, or something new, or something different. Working in the real world, I can say it would be much harder to find these opportunities with a full time job. University will prepare you for the real world in ways you would never expect, but only if you take an active role in that preparation.