Due date confusion

Hi so Im pretty confused. Today I met my obgyn and she was wonderful. I went in assuming I was 19+1, but knew our due date wasn’t solidified. Based off my LMP it was Jan 5, but based off the first ultrasound it was Jan 12. So after the examine she told us she was setting the due date to Jan 5, making me 20 weeks. It wasn’t until we left the appointment that we realized she said that the first ultrasound is what’s most accurate and that was what she was deciding from, and by the feel of my belly I’m 20 weeks. But the ultrasound is what was Jan 12, not the 5. So I’m wondering if she misspoke? I know it doesn’t matter because this baby is coming when it comes, but I’d like to know if I’m 19 or 20 weeks lol. What do you guys think?