Damn, you're discouraged from telling anyone before making it through the questions first and your mom is already spreading the word. Granny hasn't come yet and will be out nothing if you change your mind now. Your mom is just using that as leverage.
In the end, do what you have to in order to make it through. Your parents will shun you eventually regardless. Like my parents and those of many other JWs, they only love you as a JW. The religion is the basis, the beginning and end. It is always in the middle.
In the end you don't have to get dunked. Nobody can physically force you. It's all a matter of which consequences you want to face. Again, you've been put in an unfair place like so many other young ones.