You are making things difficult for yourself, it doesn't have to be like that. Saying that you "can't take it anymore" is a self fulfilling prophecy and set you up to make some very bad decisions. Step back from that and change the dialog in your head to "I am very frustrated right now, but I can do this". Develop some strength of character and focus on your schoolwork and prepare for your future life. I know a year seems like forever, but it will pass and if you are focusing on your goals it will pass that much quicker. Learning to deal with stress and channel your energies appropriately is a valuable life lesson.
Every seventeen year old feels frustration at being close to adult hood but still having to be under their parents rules, being a JW just adds another level of complexity to the whole mix. If you feel you have to tell them your true feelings, then do so, but be aware that it could make your situation much more difficult in the coming year, depending on how they react. Yes, your parents will be disappointed if you express your true feelings, but that doesn't mean their love is conditional, only that they want what's they believe to be best for you. No matter what happens, show respect and love to them, you do owe them that.