to want at least one of each gender. I have two girls and of course hoping for a boy but would be very happy with another girl. I had my u's at about the same time as you and they wouldn't even guess, so that was annoying. 60/40 odds aren't great so I would get too uptight about it at this point.
Also, I had the same experience, the tech really couldn't get the measurement until I emptied my bladder, it was really annoying. I think if you are relatively thin then you don't really need the liquid and sometimes it causes a problem. And yes, you show much earlier in subseqent pregnancies, which is kind of a bummer if you aren't ready to tell people yet. Glad the scan went well.