I would imagine that most people who want large one gender families do so purely out of fear either from past experiences or gender stereotypes. Having so little exposure to males in your family must make them feel very foreign to you. The best way to get over your fear is to face it.
Whilst i know i am supposed to say i hope you get a girl, i can't help but think having a boy would be good for your family, so you could all understand first hand how beautiful boys can. One of my close friends had 2 girls and desperately wanted her surprise #3 to be a girl, turned out to be a boy, and she says often that she thanks God she had the opportunity to mother a boy and all of her fears have disappeared.
Most of all i genuinely hope you find peace and happiness whatever gender the baby is.