Welcome to the site Jdash!
I echo Pale Emperor's thoughts that it's great that you have woken up at a young age. Well done!
The practical things about leaving the cult are a bit more problematical but will only last for a short while. Can you simply lie low and do the absolute minimum before you leave home and avoid preaching. Really--how can anyone be forced to preach something they don't believe in?
Are your grandparents reasoning people or just dyed in the wool JWs? Could you perhaps agree to just go to one meeting a week for their sake? But don't get involved in doctrine or say anything against the JW org; it will only get you disfellowshipped. Whatever you do prepare for college and try and get a part time job to support yourself. College education, especially in the humanities, is the antidote to JW fantasies and eventually whatever you study, it will prove be a sound investment to pay you your living expenses in the future!
Friends are very important, make friends with sensible non JWs whose company will further your college interests.
And do keep in touch with us.