Ultrasound dating me 2 weeks behind?

Mariah • 23, Married💍 Two miscarriages, Rainbow on the way, August 2019🤞🏼 Baby Dust💚

I had my dating scan today. It says I’m 6+5 but by my period I should be 8+5. We saw the heart beat. I’ve had two previous miscarriages, so I’m scared 😩 I thought we were almost in the safe zone.