It's YOUR life. It isn't up to your parents how you live it - though I'm sure that they think they have your best interests at heart.
Don't have a termination that you don't want.
First thing, take a bit of time to get used to the idea yourself, so that you can speak more calmly when it comes to telling people.
Don't feel pressured into telling your parents anything until you're ready.
Talk to family members who will LISTEN to you first. Not necessarily agree with you, but those who will respect your point of view and let you discuss things with them.
Re your boyfriend, it sounds like you don't have many illusions about him! You can see why your parents don't have any faith in him. That's good, you know. Keep your wits about you and just remember that, at the same time as seeing the good in someone (as you do with him, he's a lucky man!) it's ALWAYS best not to let what you want to see get in the way of what's actually there. If he treats you well - that's brilliant. But if he starts to let you down, don't feel you have to stay in the relationship to be a good mother, or to not let your parents be proved right.
If you keep your baby, as it sounds like you will, I'm sure you'll do fine.