Do not feel like you have to be in a study group to be successful. Study groups are beneficial for many students, providing additional learning opportunities, accountability, and social support, but some students prefer studying alone. You may want a study group for some classes but not for others. Some students wait until the latter half of the semester to use a study group for review.
You are responsible for your own learning (and your own test taking!). Time is short; do not spend it in an unhelpful group. It is OK to leave groups and form new ones (or study solo), provided you are respectful and open with the other members of the group.