Gender Disappointment - I feel guilty for it

Ive dreamed of having a little girl for as long as I can remember and so has my husband. I found found out this week Im having a boy. I feel like a horrible person for feeling sad about it, especially because it took a year of trying to even get pregnant. Dont get me wrong I love my baby already but Im sad its not a girl. I want to be over the moon about my baby but I find myself crying about it throughout the day. I have moments where I "window shopping" online for baby boy clothing and Im happy but then Im sad. I feel like such an awful person and mom. I feel guilty. Am I horrible for being sad about my baby boy to be???