I did my first two supported rides this summer.
Before that it was just with my husband and me & sometimes a few of his friends.
I was also real nervous about riding with people I didn't know and not being able to make it.
The first ride was a two day 90 mile mt. bike ride over some big passes. I ended up walking some and getting a lift on the support ATV both days, but in the end I had ridden 84 miles of it ,and found everyone to be real nice and supportive.
The next one last weekend and was on a road bike ( I just got into road biking so this ride really had me nervous ) it was a 14 1/2 mile ride up to Bogus Basin Ski Resort, I made and had alot of fun .(The down hill was a blast)
I learned that I am stronger then I thought and it was fun even though I was the slowest person there LOL
You will do great ,have fun.