I guess I got lucky with my parents. When I was 15 I told my parents that I didn't believe in god while we were riding in the car to church and they never made me go again. I would suggest a civil conversation on the matter, but since they are to the point of making you sign a contract I'm assuming something like that has been tried. Here's what you can do - Tell them that you want to tear up the contract and if god really wants you to go to church he will stop you from doing so. Then take it from them and tear it up in front of them.
Even if the open windows of science at first make us shiver after the cozy indoor warmth of traditional humanizing myths, in the end the fresh air brings vigor, and the great spaces have a splendor of their own - Bertrand Russell
