Please help 😣 8 weeks and baby measured 10 days behind.

I had my first ultrasound at 6w2d but they only saw my sac and yolk sac. I went back six days later at 7w1d and they saw the baby and the heartbeat through trans abdominal ultrasound but the baby only measured 0.57 cm (6w1d). I got worried about the baby size so I had a third ultrasound done today (10 days after my last one) at a different clinic, this time they did a transvaginal scan. I could see the baby and heartbeat but it confused me even more because the baby only measured 0.65 cm (6w4d). If I go by LMP (April 13th), I’m supposed to be 8 weeks today! I tested positive on May 7th. I can’t be 6.5 weeks, can I? And there’s no way my baby only grew less than 1 mm in 10 days. I’m more confused and worried than ever. Does anyone experience something similar? Or is there an ultrasound technician here who can help explain things? Any explanation, similar story, or opinion would be greatly appreciated! 🙏