I felt like that for a very long time, and still do sometimes. Sometimes it helps just to hear these words: "You aren't alone, you aren't the only one going through this. We are here for you."
I haven't had the pleasure of speaking with a gender therapist yet, but I would like to and would recommend the same to you, basically just seconding what's said in the posts above.
The hardest thing to do now may make life easier in the end- just telling your parents that you're having thoughts and doubts and interests. You never really know how they will react, and if you tell them in the way Moni suggested, it kind of eases them into the idea rather than dumping a bucket of ice water on their head. Also, it could potentially accomplish two things at once: first, you get past the anxiety of "what will they say?" that will plague you until the moment comes. Sometimes knowing, whatever the outcome, is a good way to eliminate some of the stresses that come with these kinds of things. Second, assuming a positive outcome, you may gain a very important supporter, or two, that you may not have had otherwise. Having a support system is a crucial aspect in life, and especially important during the rough times in life. If they can be there for you, let them. Give them the chance. If they don't fully take it at first, hopefully they'll come around someday. And until then, you need to have someone there for you- it could end up being a therapist, teacher, or a friend- and you have to get out of the house to get those things. You have to be somewhat social to have positive influences in your life who help you figure out who you are. I'm not saying you have to be the life of the party or in the spotlight at school, but just surround yourself with a few close friends who make you happy and who you can trust.
And again, we are here for you, and will be here with you, whatever happens.
-Dustin