Narcidius, I don't know if someone has already said this, but there's no point in feeling guilty about your identity. The longer you feel guilty about it, the more you reject the fact that you can't change the way you are, and the way you love. If my mother gave birth to a blue-eyed baby, and its eyes turned brown after four years, it wouldn't be fair of my mom to be disappointed in that baby.
In my opinion, I think you should tell your parents the truth. Being truthful to your parents is more important than anything else, especially if you don't think they would get angry or anything.
Besides, there's plenty of ways to pass on your family line if you're gay =D Apparently, you can get a girl pregnant just by inserting a finger with semen on it *) So don't worry, you're still a perfectly healthy, normal kid, capable of reproducing and everything, and there's no reason for anyone to be disappointed in you. Kay?
Good luck with whatever you decide!
Lots of hugs ,
Tony