6 week 2 day ultrasound, no baby just sac

I went to my first ultrasound appointment when I was 6 weeks and 1 day.. The ultrasound showed only a sac and no baby. I have another ultrasound scheduled in 2 weeks to check. However, my hcg came back from that day as 16,500. With that level, shouldn’t the embryo be visible by then? I’m freaking out since I just had a miscarriage in July.