First of all, relax. Take a deep breath, smoke a doobie or do whatever you have to do to just RELAX!
Just because you received a B+ doesn't mean you won't get into medical school. Your GPA is still good and you're just a freshmen too, no need to be this neurotic. You are doing just fine, continue to receive high grades from here on out and kill the MCAT.
As for your EC's, there's no need to be rushing everything at once, you should stick to the volunteering you're doing now. Next year you can focus on adding shadowing and if you really want research. Just relax and have fun.