16 Weeks - Do boys and girls still have nubs?


I had an ultrasound today. Right when she turned on the machine the babys legs were wide open facing us. I feel like I saw what looked like to me boy parts. Its shocked me how clearly I saw it. My appt to find out the gender is in 4 weeks. My Dr said it looks like a boy but its not 100% since the baby is only 16 weeks. My question is do boys and girls have nubs still at 16 weeks? Should I take what I saw with a grain of salt?