TigerMom, I think it is a good thing that you are starting out with group rides. I've been riding for two full years now, but I've probably done no more than 12-15 group rides. Most of my riding is solo - whether on road or mountain biking. There is only one way to get used to group riding and that is to, well, ride in groups. You are taking a wiser approach than I did

As you get more comfortable riding in general the things that trouble you know will pass. I remember when I didn't dare move a hand off a bar, and even drinking from my Camelbak was a challenge. Now I can do everything I want with my left hand - the right not so much, but I did focus on moving my left hand to keep myself from grabbing a handful of front brake.

Small groups are certainly less intimidating than larger, and not all groups ride close to each other. If you are more comfortable in the back, then stay there - just make certain you have a map or know the way back to your car if you should get accidentally dropped. Congratulations on your progress and keep riding