Your studies should come first (and fun – do not forget to have fun!). As obviously intelligent as you are, I’m certain you can maintain or improve that GPA and achieve some good test scores by applying a bit of academic elbow grease.
Do try to join a club or two, but don’t choose arbitrarily; rather, choose a club you might enjoy. You are into piano – are there music- or art-related clubs at your school? If so, it might be worthwhile to look into them. The same goes for other interests of yours: if there is a club for it, or for a related activity, check it out.