Well, in spite of the fact that you didn't make it the whole way to the 100-mi finish line, I think your first shot at doing a century sounds great! You learned a bunch of really useful stuff about your bike fit (or, better, lack of fit!) Knowing now what needs to be tweaked will pay dividends the next time you set out to do any long ride.

As for keeping up with your team mates, next time you might think about simply 'riding your own ride' at a pace that works for you. When I started riding a couple of years ago and realized (quickly) that I'm a fairly slow rider, I gave myself permission---yay!---not to feel pressured to keep up with anybody else, particularly on long jaunts.

I'm doing the MS150 this weekend and my half dozen team mates all know that I'll be waving a cheerful goodbye to them less than two minutes after we pull out together as a group. Their average is easily 4-5mph faster than mine! I wouldn't make it 10 miles at their pace!

Congrats on your first effort!! (And thank heaven that ditzy driver didn't do you in!)