Posted: 12/06/2013 at 20:47
I'm guessing you're in your late teens/early 20s?
I agree with Millsy and Meldy that you should concentrate on going longer. Try going out for 30mins at a pace at which you can hold a conversation. If you can't speak, you're going too fast for your current level of fitness and will gain no benefit. Aim for every other day or perhaps 2 on, 1 off depending on how hard/easy you find it.
Come the day, ignore what everyone else is doing, try to stay relaxed and concentrate on your own 'race'. Absolutely do not try and keep up with everyone else from the off or you will likely grind to a very painful halt before the end. You will probably find that the adrenaline of the day will give you a boost and enable you to run faster than you have been in preparation.