I say don't worry about it. I had a study group all through law school and liked it, but that was mostly because it motivated me to study the material on my own so I was prepared for the study group meeting. Most of the actual learning occurred outside the group.
I'd say that the vast majority of law students, including the successful ones, quit doing study groups after the first semester. Most people find them to be a waste of time.
Also--the only thing our group did was meet for a marathon session (one to three LONG days) a couple of days before the exam, going though our outlines and making sure we understood every rules and case. That's the kind of study group you can form closer to finals. But again, I don't think it's necessary.