is it ok to say you are nervous at a job interview?

I would't speak any ensecurities at an interview. Here are some suggestions to keep calm. Before you go take a bath in epsom salt. You will feel extremly calm. Also make sure to eat before you go so you don't get nausous. Avoid caffine. Set out your clothes the day before (shoes and all) make sure you have copies of your resume along with notebook paper and a pen. Do research on the company before you go. Quick google search would be great. Reading their company profile will help you come up with some questions to ask. For example (lets say its a professional position) you can say "i see on your webiste you've been in business for XX years, can you tell me a little bit about the growth this department has experienced?" Speaking of role playing, if you have someone you could practice with first that would help get over the nerves. You can google "interview questions" just so you have a headsup.

If the job is customer facing or similiar then make sure you don't cover up. Be natural, however that is. If you are right for the job youll walk it.

Try your absolute best to hide it, a competent interviewer can smell fear from a mile away.

No. You want to seem like a strong, and powerful candidate for the job. No somebody who is conquered by that stuff.