Ultrasound at 5 weeks 3 days

I had my first ultrasound this morning and I thought I am 7 weeks 4 days but baby measures for 5 weeks 3 days- has that happened to anyone? At first it looked like there is nothing there and made me really worried but then she zoomed in and we have noticed this little miracle and flickering little heart ❤️. She said the heart rate is at 90 and she would like to see it around 120 so I am going back next week to see how things are progressing. So much emotions but that beating heart fills me up with hope!