I'm so sorry you didn't get the gender you were swaying for :( I know how hard that can be, and how you then feel guilty for feeling angry or sad. On top of all that, you are pregnant, so any emotion you feel will be magnified. Of course you will love your baby but your heart still longs to ALSO have a little girl. I am not sure what I could possibly say to make you feel better, but I will say what helped take off SOME of the hurt when finding out I was having a boy when I was having a girl. Shopping. Though you probably have a ton of hand-me-downs, it might help you get excited for the baby if you could go find some new cute boy clothes and do some decorating.
Some other things you might consider if you don't want to try for a 5th child, would be babysitting someone's little girl long-term (this would only work if it wouldn't feel like a "reminder"; it could go either way. I personally am happy being like a "second mother" to other people's children, but some people DON'T feel that way). I don't know if adoption is an option for you either. I hope you are blessed either with a little girl when you try again or with a plethora of granddaughters.
I am so sorry for what you are going through right now. Don't let anyone make you feel bad for having your feelings or let what they might think impact how you think of yourself and you situation right now. It's completely normal to be upset. I think there are probably even a lot of people who get just as upset as you but never tell a soul; i think it's good that you are talking about how you feel. I hope your spirits lift soon.
DS1 (2005), DD1 (2006), DS2 (2008) and my SUCCESSFUL sway baby DD2 (due August 2013) !