I have done one organized ride so far, and consider myself something of an introvert as well. Making friends at the start seemed impractical, as everyone is focused on their pre-ride stuff. But riding along it becomes easy. Groups form and dissolve, and reform later. You will find the first SAG stop to be a much cheerier spot than the start, and they get cheerier as they get farther on.

Even if you talk to no one, I found the constant line of people about a great enticement to continue. A rider on the horizon is a wonderful reason to keep pedaling. Enjoy it.