(((hugs)))
Give yourself time, and don't google. No one puts a blog post "they saw this on the scan and it turned out to be no big deal" so you always see worst case.
At our 20 week scan we learnt that dd2 was missing her hand. We were booked straight in the next day to see the consultant and the specialist hospital the next week.
Nothing can prepare you for the moment you realise it isn't all well. For me, it was like grieving for the baby I thought I had, and adjusting to the new baby.
I went through denial (maybe they're wrong), and then sadness, before desperately trying to change the world for her-I planned a whole adapted home, which dh (much more practical than me) said "let's wait and see what she needs" and I was so cross with him for not doing it because we had to make everything perfect for her. He was right-we didn't need one of the adaptions I'd planned.
One thing I was grateful (later) was that no one mentioned termination. We wouldn't have considered it, but it would have made her feel more like a mistake than a person, so I agree with how you're feeling about that.
There were worries I couldn't express to people-would I reject her when I saw her? Would I be able to look at her little arm? I even wished it was her leg so it could be hidden easier in a sleepsuit.
When she came out it didn't matter. I don't think I noticed her arm when they gave her to me (she did scream at about 60 decibels for about 2 hours!) and I cuddled her and it didn't matter any more.
The hardest time was waiting and not knowing. It could have been much worse than just her arm, there are conditions connected to it. They're very rare, but you still have the possibility. And the worries I had that I daren't express to anyone, and even if I had, nothing they could have said would have taken them away.
I can think about after the birth fine, but remembering the dark time between finding out and birth is hard even now.
She's 13yo now and I can't imagine her with two hands. She has had lots of advantages as well as disadvantages and would be a totally different person if she hadn't had that.
((hugs))