When they say "boy" you aren't looking for a penis - it's testicles that they're seeing, so what you think may be a penis could, in fact, be an umbillical cord. I was told and shown at 13.5 weeks this baby's testicles (clear as day, exact same as the shot from 18 weeks with DS1) and she also showed me the umbillical cord in comparison.

Post a pic of your u/s so we can have a sticky beak!