Think of it this way, rather than be intimidated, consider your upcoming interview as an amazing opportunity. Since you're OOR and still got an interview, that means they really like you and your MCAT/GPA/activities have definitely gotten the attention of the adcom ... now is the time to seal the deal.
What I can't stress enough is walking in to your meeting ready to devour the interview, rather than having it attack you. I think that's why I had to re-apply before getting in. You have to walk in there as someone that they can see being a physician. Is this person confident/self assured enough to be a doc? Can they express themselves coherently? Can the candidate think on his/her feet and come to a conclusion, and perhaps most importantly, defend it? Are they self aware of his/her own strengths/weaknesses? Another thing that they will do is make you reason out a dilemma in front of them ... don't get rattled. The best advice I can offer is if you don't know, either say you don't know, or take a second to take a deep breath and collect your thoughts before launching into your views. A little bit of silence while you contemplate isn't a bad thing ... it's much better than talking yourself into a corner.
Oh oh! One quick note, if you have done any research, be sure not to use too much jargon. Be able to explain it simple terms that your 13 year old cousin could understand. If you can't simplify your research into easy to digest morsels, how on earth will you be able to explain a complicated medical condition/treatment to your future patients?
Hope this helps you relax.
If you can see yourself rocking the interview in your mind, it will happen.