Measuring 6 days behind :/

I had my first ultrasound today! LMP had me at 7+1, but I know I ovulate 3-4 days late, so I should be around 6+5.

At the ultrasound, it took her a few minutes to find the tiny baby, but once she did I was measuring 6+2 (although the first thing she said was only sac measuring at 5 weeks 😒). Could 6+2 be off? Should I be worried that it’s a little farther behind that based on my OPKs?

The doctor seemed congratulatory, and showed me how there was blood flow to baby but too small to get a reading on heart rate. But ugh I’m a mess! I want to be farther along!