First scan showed sac but no baby....

Ladies- I went to my first appt today with the expectation that I would see my little peanut and maybe even hear a heartbeat. However, when my ultrasound started, the tech was able to find the sac but couldn't not see anything in the sac. They said I could have miscalculated and be earlier in pregnancy than I thought or that my baby isn't developing properly. I have more blood work and another US next week to learn more. My question is... has this happened to you? Of course I am trying to be optimistic.. but you know how it goes.. Any insight is greatly appreciated!