Faith,
You are taking a chance doing volunteer work. This can equal the real thing in SSA eyes. You are keeping to a schedule, and are doing certain duties. You are saying I can not work a regular job, where I stand, stoop, lift, bend etc, but can do these things as a volunteer. You are risking a denial.
I suggest you find the 3373, and 3380 forms, and see what questions they ask about your daily activities.