6wks4d no baby, just sac. Don't know what to think..

I went in for my 1st Dr's appointment today and I'll admit, I left a little worried. They did an ultrasound and no heartbeat was detected, all they were able to see was the sac and the yolk. The tech told me it looked good and it's 90% that it was still too early. I went thru a miscarriage so I still have that scare in the back of my mind. They drew some blood and they want me to go back on Wednesday for more bloodwork. I'm trying to stay positive and not worry, but I can't help but feel this pregnancy is heading towards a miscarriage :( I don't know what to think or feel. I don't want to get my hopes up. My husband and I had agreed this would be our last pregnancy regardless of the outcome. Im just full of emotions. I wanna know if this happened to anyone else. Has anyone gone in at 6 weeks and there was no baby, just sac and if so, did it change after a week or so??