To be honest, even when someone is actively trying to get pregnancy, it can comes as a real shock. Maybe it happens on the first cycle they try, and they think "woah, didn't think it would happen so fast, it's too soon!". Maybe they've been trying for ages and when it happens, they are too scared to believe it's really.
You've got the double whammy of total shock as you weren't trying and the previous decision not to have children. I'm not surprised you're reeling.
But not to be bouncing around with joy it TOTALLY normal and you are 100% allowed to feel like that. Don't guilt trip yourself for reacting this way.
I would say, try not to rush the decision. You have some time to think this through. You need to think about the pros and cons of having this child in your life, how you might cope with an abortion (even if it's the right decision, it will affect you and will always be something you'll remember) etc. Also consider that this may be your only chance to have a child together, and even if you decide to abort now, this experience may change your feeling on the matter going forward. Could you live with it if you abort, then realise you want a child and then can't get pregnant? I'm just bringing up things to think about, I'm not trying to sway you either way.
While your husband's views do matter (it's his child too), it's helpful he's being supportive - although it may feel the pressure of the decision is being lumped on you? To be fair, you are the person who will need to carry this baby and give birth to it, so it needs to be something you want to do.
It's a tough choice, but I'd really suggest just letting the shock sink in and not rushing a decision. There may even be charities with support workers you can discuss your options with?
Good luck, whatever you decide.