Well you have to be there, so you just deal with it. It's normal to get nervous before the unknown, but you'll never conquer anxiety unless you confront the stimulus on a regular basis. I'm about to graduate in two months [knock on wood] and clinical STILL gives me the stomach flutters when I walk into the hospital. It's because I'm still being evaluated constantly. I'm not nervous about meeting my patients, in fact, when I go into the patient's room, that's usually when I relax.
Oh and I've had MANY clinical days that made me want to walk out of the hospital and quit right then and there. Most of them during my Peds rotation. I HATED that rotation with a passion and it was like pulling teeth every minute. It's gotten better since then now that I'm back working with adults. Still, during my first Med-Surg rotation, I was so out of my element I doubted I would ever become efficient and wanted to quit, a lot. I even cried in the bathroom one of those days. You just keep pushing through.
eta: Honestly, I don't think deep down that nursing is the right field for me. I decided to go to nursing school because I loved science, and wanted to make some money with a 2 year degree. I don't have a passion for it anymore, but the thing is, I will still work my butt off because I see it as just a job, and I will do any job I am given to excellence whether I like it or not. So, no, you don't have to know all the time that nursing is the right career for you, but that doesn't mean you can't be a great student, and a good nurse.