Measuring few days behind

So I had an ultrasound at 7 weeks 1 day but I measured 2 days behind 6 weeks 6 days. Now this was transvaginal with the ultrasound tech. Today I am 8 weeks 5 days and my doctor wanted to do a quick abdominal ultrasound and I measured 4 days behind today. 8 weeks 1 day. The heart rate did go up since the last time. It was 135 and now it is 186. I am just still concerned? I had a mmc in the past and I feel like I can’t enjoy this pregnancy. Anyone else measure a few days behind and everything was okay? I am also sure of when I ovulated and it shouldn’t be off but I guess idk when implantation happened.