Don't be ashamed to admit to gender disappointment. It's a real thing. I experienced it myself last pregnancy. You can't help the way you feel--and of course, first and foremost you want a healthy baby. That goes without saying.
My SIL was told that her second baby was a girl and she wasn't even that early. I forget the gestation, but her OB was doing an u/s and told her. Several weeks later they saw a penis. Boy bits can often hide out between their legs!
I haven't seen an image however, but no matter what, do try to prepare yourself for a girl. Once you know for sure, if it is a girl, you might want to have one of those 3-D elective scans to get a look at her and begin the bonding process. I hope you do get your boy, but I have to tell you, once your baby is born its gender becomes meaningless. Really. I had a very hard time wrapping my mind around having a boy and very soon after his birth had completely forgotten about gender. You just don't care, you love them so much. Good luck!