I'm at a party and I feel nervous?!

Many people don't enjoy parties and don't feel comfortable at them. They just hide that thinking there's something less desirable about them or wrong with them, and pretend everything's fine, or they do it llong enough to figure out some way that they in particular can be comfortable.
Though many also just avoid most "parties"--especially those with no particular purpose, just partying.

Some individuals are just people-persons though, and love the feeling of "playing" with people in social situations--seldom nervous or wondering what to say next. That's not most people though.

The party could also be semi-threatening in feeling because it's dark-ish and the music is loud, and probably most of the people are at an age where they don't really know what they think, what to do, etc., and want the atmosphere (or alcohol, etc) to take care of that for them.

You should be able to make some excuse and leave now though if you want. Call someone if you need picking up and just say that the atmosphere felt threatening to you and you'd prefer to leave.

It's also possible that you have an anxiety disorder or are just especially susceptible to anxiety in many situations. In those cases, you can see a therapist for cognitive behavioral therapy to address the anxiety and learn new ways of dealing with things (and try medication as well if it's truly bad).

Many people though (often those who are more "intelligent" in a certain way, or have lots of interests in life--especially thought/brain related interests), never enjoy parties and esp. parties where the talk is "empty," and choose seldom or never to go to them once they can and are old enough to get enough experience and see what's going on and what their preferences are. They may love real *discussions* with people though, even if they don't like a lot of social chitchat.

Just relax! If you are there with friends [hopefully you aren't alone] then dance in a group. If there is drinking, remember that you don't have to be drunk or drink to have fun! But if you still feel uncomfortable, leave.

I'm in college, and I go to parties a lot

If you feel uncomfortable just leave.

I know that feeling. Listen to your gut. Go home, or just have a smoke and see what happens.