I did a century with no ride longer than about 66 miles that year. And I didn't "train." I ride lots of hills and the century was flat, but by the coast, so hence, winds. My DH told me if I didn't pull, he would kill me, that's how bad the wind was.
If you fuel/hydrate correctly and choose a moderate pace, you'll be fine. My last 15 miles were hard, mostly due to plunging temps and torrential rain for about 10 minutes. I finished in 6 hr. 33 minutes riding time, which, while not speedy, was quite acceptable.
You can do it.