Feeling worried about being a few days behind

I have my first OB appointment on the 25th so I decided to get an elective scan. We have places here that do pregnancy confirmation starting at 6 weeks. I’ve had a loss before so this makes me feel better ( I also did this with my last pregnancy)

I should be 6 weeks and 3 days today. My LMP was Dec 3rd. Baby was measuring at 6 weeks 0 days. There was a heart beat and fetal pole so I should be relived since that is why I wanted to go but now I just feel nervous. I know it is normal, this is my 3rd child so I know how pregnancy works, I know it’s normal to be off a few days but I can’t help but feel sad about it.... both of my previous kids always lined up perfectly with my LMP and what the due date should be.