5w5d ultrasound, no embryo

Ash

This is my first pregnancy, not sure if I should be worried. They told me that there is a sac but no embryo. Is this not a viable pregnancy? Should I be worried? I went because that was the only way they could confirm my pregnancy without yet another hcg test, and they didn't really say much. He also didn't seem sure that he knew what he was seeing, but seeing others ultrasound pics they look different. Definitely no embryo in the sac..sac