If your girlfriend is being paranoid, you need to confront her about it. The chances are that at your fresher's week, people will be trying to get off with you at club nights and such, so you need to explain to your girlfriend that at the end of the day, YOU are the one that she has to trust. As long as you don't get off with other people, she has no reason to be concerned.
However, having a clingy girlfriend will definitely put a dampener on your social life, especially if she's the sort who doesn't like you having friends that are girls. Seriously think about your relationship now, because if you break up before you both start uni, she'll have some time to move on and meet new people herself, whereas if you break it off at uni, things will get awkward really fast. I know several people who had relationships when they came to uni, and they had all broken up within a month because meeting so many new people tends to put a strain on a relationship. I only know one couple who remained a couple through their first year, and they only managed it because they were both anti-social and only liked spending time with each other.
So in short, think about the relationship and whether you really wanted to be tied to your girlfriend during your uni experience. I personally think breaking up might be the best option but I don't know you or your girlfriend, and you might be able to make the relationship work. It doesn't matter how much advice you get, the decision is ultimately up to you.