Measuring behind

Hey mamas. Looking for some reassurance. Went in for my 8 week scan today, and I measured 6w2d. They did a second scan and measured 6w5d. Heart rate is at 106. I know EXACTLY when I ovulated (opk tests) and when we conceived. I also found out I was pregnant 4 1/2 weeks ago (December 19th) so it’s not possible for me to only be 6 1/2 weeks along. I now have a waiting game for 2 weeks to see if baby grows and is viable. Have any of you gone through this and gone on to have a healthy pregnancy? I’m so worried and not sure what to think. Pic of my scans today. My HCG levels today were 76,068.