Join clubs? Volunteer?
Rin-chan
Joining clubs at this point is pretty silly. Colleges don't necessarily want to see that you were in a lot of clubs, but rather that you were devoted to them. Joining clubs during the past semester of high school doesn't spell devotion to the admissions department.
I would obviously write them and convey the idea that they are your first choice (if indeed that is true) and send in your grades from this semester. Keep them updated as much as possible. The more interest you show, the more likely they will call you if spots open up. Now is not the time to be silent in this process.