Says I'm 8 weeks not 9?

When I went for my first visit ever when I found out I was pregnant I was only 7 weeks2Days it showed up as 6 weeks5days the doctor said it was fine because the first day of my last menstrual was June 13th today I went to see the baby which now I'm 9 weeks and 2 days it said on the ultrasound 8 weeks and 1 day which is making no sense. Has anyone else went thru this I'm 100% sure I'm 9 weeks we've calculated