Ultrasound question.....??

Ok... I went in for an ultrasound a few weeks ago. One of the twins is definately a boy (I have 4 boys already), the other twin though not too sure. The tech was showing me that the view we had was looking straight up at the backside of the . Now we didn't see anything hanging there, but he said the view wasn't good enough to identify girl parts. How much of a chance do you think that it is a girl? Would we have seen something hanging there even with a rear under shot. I know it sounds weird or even a little funny. I am just wondering what you think the chances are. Thanks for your time and sorry if it's a silly question! = )