Anyone heard of the Nub theory? Trying to work out my baby'd gender :) Ultrascan took at 13w+5

Sophie
My baby also moves around too much to get a clear scan picture so when I went to the 20 week scan, she said possibly a girl but I've got to go back again for the measurements. Was the angle wrong to make it look a bit like a girl? Bottom view looked like a circle but the circle had a faint line in it aswell. Any help would be nice