Measuring behind

I'm supposed to be 6w6d, but at my ultrasound today the embryo measured at 5w5d and showed no heartbeat. If that date is correct I know it would be too early for a heartbeat, but I have been tracking my ovulation so I know my dates are correct. I feel like the little one stopped growing at that point and I'm now just sitting here waiting to have a miscarriage 😞. They did an HCG quant test and will do a subsequent one on Monday to see if the levels are going up or not so I know all I can do is wait. I was just wondering if anyone has had any experiences like this?