Voice your fear: ie, tell the auditor that you're rather nervous.
YOu can say it something like 'I know we've got a good system, but audit is a new thing for me/something I haven't had much experience of, and I'm feeling a bit nervous.'
Funnily enough, disclosing (ie, saying aloud that one is afraid/nervous) very often helps to settle the butterflies of nervousness. And almost every auditor (very definitely the good ones!) will be understanding and accepting of people being nervous.