What to do and how to act at a private school interview?

I have an interview at PLC Sydney tomorrow for a 100% scholarship, and I'm not sure what to do. I haven't ever been interview and I'm daunted by the very idea. Has anyone else had an interview before at a private school? I really want the opportunity to go to this prestigious private school, because it has a good academic record and amazing facilities. I don't want to make any mistakes on the day, because it just means so much to me! If I make a mistake, I won't be able to forgive myself. Ever.