nub theory _ is it accurate?

Hi all. I heard of the Ramsey theory for the 8 weeks scan but when I posted my 12 weeks scan on fb someone told me was a girl straight away based on the nub theory.... I never heard of it and wonder if it's really accurate and if my friends were right about being a girl. I already have a girl and was hoping for a boy ♥️ happy with both as long as healthy but just curious. I am now 17w6d and will find out for sure on the 28th but was just curious about your opinion on this theory. Photo of bub at 12w4d