nub theory?? Skull theory??

Sarah • Wife 8/31/18 and mother to a perfect little girl 5/31/2017 and little boy 10/4/2019. Pregnant with our 3rd Due September 2021. We were expecting twins but lost baby B early on.
I'm not sure if there is a nub in this picture. 
What are your thoughts??!!! 12 weeks 1 day!