Dates are off

So, I just had my first ultrasound with baby #3 (hopefully 2nd live birth). I measured at 6 weeks 2 days. Going off of my VERY reliable period, I was supposed to be 8 weeks 2 days. I didn’t test for ovulation, because I was supposed to be out of town for the majority of my fertile week. I know I’ve had sex quite a bit in the last month, so I guess I could’ve gotten pregnant anytime. But, I’m never off on ovulation or my period. This would’ve been a SUPER long cycle.

I found out on Christmas (3 weeks ago) that i was pregnant with a digital. I am super confused about the dates! They just don’t add up!!! Baby had a healthy heartbeat in the 130’s.

Anyone else who has been through this? I’ve had a miscarriage in the past and now I’m just concerned that something is wrong.