OK, sorry, I thought the cancer run and the Edinburgh event were different. They are the same, correct?
Why are you awake so late... nearly 1:00 AM ????
My advice to any first-time marathon runner:
First, follow a structured training program
Second, on the day of the race, run the first 10 miles slower than your planned pace. For me, the adrenaline kicked in, and I "burned out" the first 10 miles, and it cost me dearly.
But you can do it. Think positive. Do not say, "I can't..."