Can someone please explain this to me,

So when I was 5weeks and 6 days (going off calculations from last period) I went and had an early ultrasound, they told me I’m measuring at 6 weeks and 2 days, they then sent my doctor a report saying gestational age is 5weeks 6 days, so what would I really be measuring I know it’s only couple days difference but I really want to know ?? Someone please clear this up for me Thankyou 😫💞