Gender prediction correct?

I'm 17 weeks pregnant and Wednesday I went for a check up at my drs office(they aren't gunna do my next ultrasound until 20 weeks for gender prediction) well I work at a hospital and was just curious so I had one if the ultrasound tecs look and see what they thought..at 16w and 3 days would it have been obvious if it was a boy at this time..it was just a normal ultrasound performed...advice and stories please