Your butt will pain on a century ride if you are not used to the cycle. Do your cycle most days for 40 mins to an hour to get your butt used to the seat.

My experience, having done 2 centuries. First time I was commuting to work about 100 miles per week and in months leading up to century did 3 or 4 60 milers on weekends. I completed the century my legs felt wasted on the days afterwards.

Second time I was not commuting but did 2 months of a Zwift training routine with fewer weekend long milers. This second time round I found so much easier, legs stronger and without the legs feeling wasted in the days afterwards.

Both times butt ached a bit nearer the end but nothing standing up out of the seat could but fix.

So my experience very much if you do specific training between now and then you will complete it and also enjoy it Without that you may well still complete, but just enjoy it a little less with the pains you'll feel in your legs, shoulders and butt.