Jim: I take 6 gels and energy drink during the marathon, starting at 15k and every 5k after that, so it seems your 8 gels is not too much and if you are running strong at the end you know you have got your training and your nutrition right for you.
John: Cramp can be a number of things. It can be nerve related, so could be worth getting your back check, it could be de-hydration, or fatigue, the best thing I can say is to drink an electrolyte drink in the days leading up to the marathon, and ensure you have a good hydration strategy during the race. Good luck! I am sure you will make that finish line.