Hey OP, I completely understand. When I was pregnant with my son, we found at at 20 weeks it was a boy. I had no idea how or why I had such a strong reaction, but I burst into tears.
After trying to process the feelings, I came to the conclusion that I wasn't sad to be having a boy, I was sad because I wasn't having a girl. Does that make sense? ** I love my boy with my whole heart and would walk through fire for him.
I think my feelings of sadness were because my husband isn't close to his mum, my brother isn't close to our mum. All the adult men I know are not close to their mum. My mind was fast forwarding to my son's adulthood and him abandoning me, which is totally unfair to an unborn child! On the other hand, I am very close to my mum, as are all my friends.
I now have a daughter too. I love both of my children equally, I can honestly say there is no difference to how I parent them. Nothing to do with having a mini me or dressing her in pretty dresses (she won't wear them).
My son is a mummy's boy and can't get enough mummy cuddles. My daughter couldn't give two hoots about me and purely sees me as someone to help wipe her bum, and even then only if daddy isn't around!
Take the time to work through your feelings, but I can assure you that you will love your baby, and when he arrives you'll never imagine life without him.