congrats! and I can relate to your shock, I was so convinced my DS was a girl that even during the last week of gestation, when he was over due, I had two separate dreams that "she" was a boy and when I woke up, I said, huh, funny because it's a girl. (We had kept it a surprise)
I fretted about either gender, nervous about bringing up a boy, bringing up a girl etc. But then once in my arms, the boy became a person. It really surprised me.
Now the talk of circumcision starts. LOL
Enjoy thinking in terms of "he" rather than "it"