Stop thinking about it, that may help you! I did my first century on a tandem. My 'captain' said I was riding with 1/4 of the training I needed. Yes, he told me this the week OF the ride! Turned out I did fine, no problems except I was a tad bit sore on my sitz bones-but everyone else was as well.

We started riding our next century the following day, but because of a blown tire, only got to do about 89 miles because of the time. I made it through both days, and could have gone the full 100 if it weren't for tire issues. All this with only '1/4' of the training.

I actually felt great, and had enough training to do both. You have had a lot of training and know all you need to know to get you through. Relax, and enjoy it! You will be fine!