I dont think you can tell the gender at 16 weeks using the nub theory because the "nub" has either turned into a clitoris or a penis... I'm not an expert but have been researching this as I had a gender scan at 16 weeks and wanted to make sure they got it right
Did you get a potty shot?? This would be alot better for determining what gender bubs is at 16 weeks
My scan pics should be on here if you wanna look at them and see if they looked anything like what you saw while they were doing your scan. You could also google 16 week gender scan pics.
I find out this tues if the sonographer was right for me!