Unsure if I should stop at baby number 3

Jackie • Baby #3
Me and my husband have 2 girls age 6 and 10 months and I am expecting another girl in May 2015! I am ready to grow with my three and tie my tubes and enjoy life. He wants another baby and is hoping we get a boy , but I'm not in any way willing to go for another (4) baby. Am I being selfish for not giving him his fourth baby? And not a chance at a boy? What if we do have another baby and it's another girl ? I dont know what to do , BTW I just turned 24 and he is 30?