Pretty good ride I would say but now you know where you can improve.
Your post backs my advice I have given to first time century riders over the years about when to eat. My experience is that I start to lose steam about mile 60-65. If I am on a century, I plan my meal at mile 60 "BEFORE" I start to lose steam. I eat something solid like a turkey sandwich. I did 23 centuries in one year and every single one of them was the same story. I learned when to eat.
Then I remount and back the pace of for 10 miles or so, relax and warm back up into a good spin. Then mile 80-85, I actually start feeling strong. Mile 95, I actually finish off with a strong sprint the final 5 miles. An amazing feeling when planned just right.
BTW, I start off at an easy pace. That is one mistake too many riders make when riding an organized ride. All take off like a bat our of hell. They do well for 20-30 miles but then burn out and struggle the rest of the way. I'm usually behind at the start warming up into my pace. Somewhere along the way, you end up passing all those bats with a consistent pace.
For a first century I think you did very well as most are a learning experience or experiment process moving on to bigger and better things.