I used to be worried about my first century. I ride a lot now like 150 miles a week, but before that I had only done my longest ride at 70 miles. Someone told me I would be fine. If I could do 70 miles alone, 100 with a pack would be a piece of cake. You draft, there is adrenaline from everyone else, and excitement, lots of refuels stations, you stay hydrated. They were right, the 112 miles were so much easier than the 80 I trained for alone. Hope that helps and gives you motivations. Centuries are so much fun! Give it a try. There is always a sag wagon.