not a teen but if i can offer my piece of an advice, i'd rather tell both him and your parents asap.
especially because the first tri is a tough and delicate time if you're pregnant, and a hell if you miscarry. miscarriage is a no joke and if you don't tell anyone you'll cut yourself off any support system you will need.
plus, i rather think he'll feel like you're lying and trying to "trap" him if at one point you say: "you know, i've been pregnant from you but i haven't told you and i miscarried" rather than telling him "hey, i know this is a hard news, but i'm pregnant with your baby. i don't expect you to get back with me just for this reason, or to be involved in its life, nor i'm trying to "trap" you, but i feel you need to know."
it is HIS responsibility too, having chosen to have unprotected sex with you. it's 50-50% yours and his, and the whole "trying to trap a guy" logic is a last century thing that should be banned. Guys need to take full responsibility of their actions as well and mind the contraception business themselves as well if they don't want babies too early. So get the whole "trapping him" business out of your head, you haven't planned or thought to be here at 17, just as he didn't at 18. That makes you two the same and you both have to deal with it.
Also, i find that waiting for the first three months to pass before telling him is a really bad idea. he may take THAT as being fooled and tricked and lied to. If you let him know now, you'll also give him more time to get adjusted to the idea and deal with it. You'll also make him feel he has some options with keeping the baby or not (i mean, it is your call in the end, whether to keep the baby or not, but at least there is SOME possibility you leave him to at least say his word, if you let him know before 12 weeks, even though it may not be what you want to hear. but i think it is important for your future relationship. and that's what you need to keep in mind, as children are a bond forever, whether you like it or not.)