I'm not sure if you have already had the interview and thought you were too nervous or if you are about to have the interview and are worried that you will be too nervous.
If you have already had the interview, just remember that they asked you to come. That must mean that they liked what they read about you.
If you haven't gone, then stay positive. Think about your strengths and list them. Be prepared. Smile and look confident even though you aren't.
I hope that covers all possibilities