Joining the UAS requires you to have a least 3 semesters left to study at university, it may be that a year placement in a 3 year course (I assume its a 3 year course) somehow disqualifies you from getting a place i.e. only attending for two semesters then going on placement. Someone with a little more knowledge can confirm or deny this but it may be that it was no fault on your part that you didnt get in it but the timings of your course. As everyone said keep trying dont let this setback get you down too much.