6 week ultrasound

Kaitlyn • two losses before our double rainbow on 5.31.2017. 🌈 Expecting again on 12.4.2018! 💕
So based on my last cycle on March 4th my OB said I would 7weeks 5days today. Putting my due date at December 9th. Well, I went in for an early ultrasound and the technician said baby is measuring only at 6 weeks. So does this mean my due date will be around the 21st of December then? 
Here is our little babe at exactly 6 weeks. Yolk sac and fetal pole and baby. She said all looks healthy. What did your 6 week ultrasound look like?? Similar?