First of all, finding a calling to serve is not a religious thing, at least not in my books. I am an atheist yet still feel a need to help my fellow mankind.

My anxiety is getting in the way of doing so. Mostly the anxiety is performance related. What I have done is sign up to be an on call volunteer. I do special occasions with my support group, a museum, several health related fundraising campaigns, and a street worker program. It means I only end up giving my time once per month. Yet, even this is gratifying and I believe the intent to help is equally important.

It sounds like you have such intent and have already done more than I think people would expect of you. By the way, it is alright to say 'no'. Say yes to what feels a good fit for you.