If you've already committed to a volunteering a certain amount of time with Americorps, failing to honor that commitment will not look good. If anything, it looks like you are good on the clinical experience (200 hours of shadowing is waaay more than enough) and need more community service, so sticking with Americorps is probably the best way to strengthen your application.
I don't think you should be worried about having too few interview invites. There is still plenty of time. You can worry if you still only have a couple of invites by mid February.