I'm not homosexual, not hetero, not bi, but I'm...Nonsexual?

Your still young at 17, so you might not want sex now, but that's not to say you won't want to in a few years time. There's nothing wrong with not wanting to have sex, and you may well be asexual. But just don't stick a label around your neck yet, keep an open mind. If you get to know someone closely at some point you might find that your attracted to them, and your opinion might change.