How can I make myself happy about having a boy?

This is my 4th and last child. We already have a girl and then 2 boys. I love all of my children but really wanted a girl. This baby was an accident, proof that birth control isn't 100%. So not only am I having to deal with baby coming earlier than I had planned, but today I found out he is definitely a boy. He's healthy and I know that's important, and I'm sure I'll grow to love him, but right now I am very disappointed. My husband didn't care either way, my daughter is disappointed she didn't get a sister and all I can think about is that my youngest boy is so much of a handful I don't know how I am going to cope if this baby is anything like him. I am trying to think positively but I really just want to cry. I am not looking forward to this baby at all, any advice on how to change my thinking? If this had been a girl I would be over the moon, but now I am so depressed.