so I have to do a church service every Sunday, so I naturally put "unavailable" in my schedule, but after a few weeks I was schedule for Sunday, so on Saturday I called in to let them know that I wasn't showing up on Sunday, so how much trouble am I in?
Don't worry about it because they can't do anything about it. You have Sundays off for religious reasons and it it is for a religious reason they cant do anything about it pretty sure you could sue them for discrimination or something like that if they did try to fire our or do something about you not showing up.
Yeah, technically if it's an "unavailable" day, then they're not supposed to schedule you. And you also gave them ample time to find a replacement, so busy day or not, if they can't find someone else, then it's on them.
However...this may all go out the window if you're still in probation time.