Gestational sac and yolk sac

I was just wondering if anyone else experienced what I am, I had an ultrasound done yesterday with blood work and my levels came back around 27,000. My OB called today and they only saw the gestational and yolk sac but no fetal pole or heartbeat. I have an appointment in 11 days for a follow up ultrasound cause if things are progressing they should be able to see everything else. They said I might not be as far along as we thought. Has this happened to anyone else?