group rides seem intimidating (Washington DC/Silver Spring, MD)

[rain]

Here's my story:
I've been riding for several - maybe 7 - 8 years in the Washington DC metro area. I'm a slow learner, ride somewhere between 12 - 16 mph, but I've come a long way given my set of challenges and I think I've got a lot more in me, certainly if nothing else, I'd like to ride til I'm 80. I can ride further but I don't trust my skills so I've stuck to ~30 mile rides on Beach Drive (Washington DC) because it's a known bike route and if something happened a helpful (probably male) cyclist would stop. Plus it would be easy to call a cab.

But the prospect of doing that for another year has me ready to quit (I'm being dramatic but I'm frustrated.) It's just too short of a ride and I'm not learning new skills. Yet, I have no idea how to go about joining a group.

The one group ride I did was a D ride. It was fun, there were not enough people and I learned nothing. And logistically it was hard to get to.

I would really appreciate your tips and suggestions. I ride slowly but I'm not a casual rider, and that's where I'm not sure what to do. I also (another source of frustration) don't have any friends that ride so I'll be joining this group on my own so I'm looking to start slow.

Fearful but ready to plunge!