Gestational Sac but no embryo/fetal pole

So, I went to the doctor today because of some super light spotting I had this morning and over the last few days, they checked and told me it looked okay and just was just old blood. They also sent me to get an ultrasound, and even though I should be 7 weeks 2 days according to my last known period, the scan only showed an empty gestational sac measuring 6 weeks. I was then sent back to the doctors office to have blood drawn to check my HCG levels, and will have to go again for more bloodwork in 2 days. I am trying to have hope for my baby that maybe the dates are just off but I don’t know how common this is. 😢