Due Date?

Catrina • 25. Married to my other half. 5-15-15. 1 angel baby named River. Daughter named Remington. Son named Journey.
Had my first appointment today and my baby measured at 6 weeks and 6 days but she kept my due date at feburary 26th which would put me at 7 weeks and 3 days. She said she was putting my due date at the start or my last period but my baby measures 6 weeks and 6 days. Is that normal?? 
So should I go with Feburary 26th or March 1st? 
Baby had a healthy heart beat and my little bean was so cute!