Assuming I have understood correctly you have no problem running the 13.1 miles as you are regularly running up to 10 and ran the half distance twice last week.
With the time you have left there isn't much more you can do! Make your last long run at least a week before the race and just a couple of easy runs in the last week. 6 milers would be good.
Last couple of days don't run, eat well, sleep well drink plenty of water and stay out the pub.
On race day don't go off too fast, start at your usual pace and pick it up later if you are feeling strong.
Other than that don't change anything this clse to the race as it is more likely to do harm than good! If you enjoy it and want to race again give your self a bit more time to change your training if you want to improve performance.
Based on what you have stated in your posts you'll be fine and will do your cause proud.
Edited: 25/09/2012 at 08:57
