Is my due date from LMP or what the baby is measuring at?

Ka
Hi everyone. I'm a little confused. I was technically 6 weeks & 1 day on Monday when I went to my first prenatal appointment. The baby was measuring at 6 weeks & 4 days. The due date didn't move dramatically. It went from august 13, 2017 to August 10, 2017. If I put august 10th into Glow, it puts me st 6 weeks & 6 days today. My LMP puts me at 6 weeks & 3 days today. Which do I go by? Thank you!! Sorry if there's confusion ☺️ FTM.