Scans and dates

Courtney • Due with baby #1. May 2020🤰🏻💜🙏

I had a dating scan back at 6 weeks ish. When they said I was only 6 weeks and x days I thought I should've been 7 weeks and a few days. Due to period and ovulation. So they stuck with May 29 and that I was 6 weeks as per their scan.

I had my 13 week scan last week and they say I'm tracking 13 weeks 5 days so ahead. The Dr won't change my due date so do I plan in my head that I'm ahead or go by their date??

Anyone else have this happen? Thanks :)