Thanks for the advice everyone.
Unfortunately I don't need an excuse to cut down on my mileage

and I never ever knew that two weeks thing, so thanks for that too.
I haven't had much of a set routine as I work shifts, but I normally try to do a long run early in the week and then a few shorter ones. Most weeks I'll do maybe 2 lots of 5 miles and a 5k as well as the long run and also spend one day in the gym doing other cardio and a bit of conditioning.
I can't quite believe how far I've come if I'm honest. I entered because I life was a bit stagnant and I was miserable - I literally couldn't even manage a mile - and just wanted something to aim for. It's been really great for my confidence and general happiness
Tamara: If you can get up to 10 miles the week before I think you'll be fine. Especially if yu've faced adversity the feeling of how much you've achieved despite that will be immense!
So from what you all say, I should be fine. I just hope I don't have a bad running day on race day. One day last week I couldn't even manage 2 miles!!