1st ultrasound help!

Hi everyone. I had my first ultrasound today. I thought I was around 7 weeks and 3 days but it turns out I’m really 6 weeks, 1 day. Has this happened to anyone else? I go back in 2 weeks. I’m so very nervous that means something is wrong. She did find a heart beat and it was 129. This is my first pregnancy so I’m a worry wart!