I actually wound up not riding today due to things not related to this.
Thank you all for your thoughts. I usually ride alone, but my really long rides have been on bike trails where I'm unlikely to get lost. I think Crankin and Indysteel hit it on the head--trying to keep up at this point would be no fun.

This group is a part of my university's club, and while it theoretically has both recreational and collegiate racing members, most of the people who ride regularly are racers. I'm slow--I can hit in the 20s with nearly no effort on flats, but it's not a sustainable pace. My group riding experience has pretty much exclusively been with the boyfriend and his family, so of course they're going to ride loosely formed and slower than normal so that I can keep up. (I actually had to tell my boyfriend to go faster last time I rode with him. He underestimates me sometimes. ) Riding with people I don't know who probably expect a higher level of performance than I think I can provide is probably not the best introduction to more "serious" group riding.

I think I'll hit some hills tomorrow and during the week, then try out the route by myself (or see if I can find my friend who helped get me into this) next weekend. It's a route the club regularly uses, and I think I can modify it a bit to make it easier to get back to my place than from the meeting place that the ride uses.