Baby behind schedule at viability scan

I had my scan yesterday to confirm viability. There was a heartbeat at 140bpm but the baby is measuring far behind schedule. I am positive of my date because I tested with strips and did temping every morning with a confirmation of ovulation at CD 16 and a positive pregnancy test at 10DPO. So I should have been 8 weeks at my scan, but baby was measuring at only 6w3d.

The ultrasound tech and my midwife said that at the moment this pregnancy is still considered viable since it is in my uterus and there is a heartbeat but that there is of course a risk of miscarriage and/or genetic defect. They encouraged me to stay positive but I can’t help feeling crushed because it doesn’t seem like there’s a way to come back from this normally. I feel like I’m just waiting to see if I miscarry. We will do a re-scan at the end of next week to see where things are, but even if baby is growing good by then, I feel like I’ll still just be waiting for the genetic screening at 11weeks to find out if anything might still be wrong. I don’t know how to go through each day and how to hold on to any hope at this point.

Has anyone gone through anything like this before and would be open to sharing your experience?