HI
if anyone is stressing about the UCAS day then dont!
Standard procedure is that they invite you onto campus before they give you an offer.
They will most likely give you a tour, take you to lunch, give you a sample lecture and tutorial, the interview is informal. I do maths and i was just asked to answer one simple question (which i got wrong) and still got a place. Offers come through within 2 weeks of ucas i believe.