You don't have to keep anything from him, and you don't have to apologize for keeping this baby. If he wasn't prepared to be a father, he should have thought about that before he got you pregnant. It's his responsibility to step up and take care of this child.
I'm not sure if you've been to a doctor yet, but you should get prenatal care. Your doctor might also request an ultrasound for fetal anomalies, just to play it safe.
It's not his decision to make you have an abortion, or to make you have this baby. It's entirely up to you. Don't apologize to him for not aborting. You're not a bad person and you did not make a mistake. Just be up front and honest about everything, and if he has a problem it's
his problem. He'll have 30 weeks to get over it.