Yeah I was thinking about this last night. I just did a 70 mile ride with roughly the same amount of climbing. Over 100 miles, it's really not bad.
Although "flat" and "hilly" are very much in the eye of the beholder, and very much related to the terrain you're used to riding. The more you're able to ride hills beforehand, the better prepared you'll be.
FWIW I've done the Sea Gull Century which is on the eastern shore of Maryland, where it really is very flat. And I hated it. It was boring and there was no opportunity to coast at all. With hills at least you get to enjoy a downhill now and then.
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles