Tami, You KNOW you can do the job!!!so that part is sewn up, convincing them may take a little bit longer but you can do it, remember YOU are interviewing THEM as much as they are interviewing you!!! You are trying to decide if YOu want to work with THEM also. I went for interview once for a job that I THOUGHT looked perfect for me,and on paper, it was. but the staff interviewing me revealed so much about the organisation and themselves as a bunch of A****oles that ,when offered it , I turned it down.
My suggestion to you is, " be as relaxed as you can be",If necessary Pause and take a coupla deep breaths before answering a question, if you are uncertain about what they are asking, ASK them to explain what they want. Uf they give you the classic " what would you do if..." be prepared to say "Refer to my supervisor" or"Look it up in the Manual"
NO one expects you to carry the complete" Rules and Regulations relating to interactions with the Public in Stae and National Parks 1978 in your head!! oh and(although I am sure it will play no part compared to your real skills and knowledge) Good Luck!!!