Everyone gets nervous/anxious/worried/excited about actually going to Uni, so the jumble of emotions you are feeling is VERY normal. For most people, this 'waiting' time is the worst bit and once you know you are going and actually get there, everything falls into place - and a few weeks into term you wonder what you were once so worried about.
However, if you really arent sure that you are holding Offers from Unis/courses you actually do want to go to, then step back and reconsider. There is nothing to stop you waiting until Results Day, seeing what happens and making a decision then to either cancel your 2013 application and reapply for 2014, or just deferring any confirmed Offer until 2014 to give yourself time to think.