I'm Christian but I honestly think you should listen to my advice. First of all, TELL YOUR PARENTS YOUR FEELINGS. 99.9% of relationships are fucked up because the communication sucks. If you don't believe in God so be it, but let your parents know. Personally, I am a firm believer in a higher being but I try to respect other people's opinions even if I don't agree that they are doing the right thing. I never try to force my religon upon other people, and I'm sure your parents won't either. You shouldn't make a big deal out of it if they are asking you to go to a mass/service/meeting, as there is nothing wrong with that. You are after all being asked, not being forced, and you can make your own concious decision as to whether or not you wanna go.
Second, the part about the car makes it seem like your mother is not a normal person to me. That has more with her being mentally crazy than religious. In my opinion, miracles of God can happen, but stuff like not wearing a seatbelt is lunacy.
As for the part about God being an asshole, it sure can seem that way sometimes. But the way I think about it, the bible never said anything about how life was going to be an easy thing, in fact, im pretty sure it said quite the opposite. So as humans, why do we expect things to be perfect when they weren't intended to be? That's an entirely differently question but I believe that it's a cornerstone of Christianity, having faith at all times, no matter what the circumstances.
Point in case, you are growing up and your mind is creating new opinions constantly. You are entitled to whatever you want to believe but remember to respect what others think, including your family. I also think your ideas about Christianity are a bit skewed. It's all about faith my friend, you either have it or you don't. You can either live the way you think God intended, with love and helping others, or you can choose not to. My suggestion would be to first tell your parents, then perhaps go to those meetings, and even read the bible. I think you will learn a lot. Good luck with whatever you choose.