It doesn't matter how qualified you are, at any new job, you're really not going to know how to do your job! What they're looking for is someone who can learn how to do it and has the proper knowledge base to do it well. They certainly would not have asked you to interview if they didn't see you had the necessary qualities.
I don't know when you're interview is, but spend your time preparing by reminding yourself of all your good qualities and how they will help you be amazing at this job. You may also want to see if one of your professors in this field would be willing to help coach you for this specific interview, as it sounds like it's your first one in the field. Practice and study! Just like for a test.
Don't sell yourself short. This is an awesome opportunity! Good luck to you.