Emmy - I think you should run at 10.45 pace on Sunday (based on your half time), there are no hills so should be fairly easy to keep a steady pace and just hold that pace as long as you can. You may well slow in the 2nd half but you'll still get a good PB.
Keith - I disagree, toilet stops are not always necessary in a marathon and as you had to stop within the first 2 miles means that you mistimed your pre race fluid intake. So there's another 2 mins to knock off your PB next time if you get the fluid right.
Khanivore - and clog your arteries
LOL