HELP! Twins? What do you see?

Safari

Hi! My doctor told me at my 7 weeks that this looks like twins with one yolk sac? We saw two heart beats...but only one sac. I just want to know if anyone has seen this? We did <a href="https://glowing.com/glow-fertility-program">IVF</a> and put in oh embryo, but it looks like it may have split! Or is it just one? Ha ha HELP!