I'm confused

According to my first doctors visit I should be 8w pregnant (just turned 8w today) & my due date is on August 12th. But on yesterday I had my first ultrasound & the tech measured my baby & said he/she measured at 7w 4d & my new due date is August 14th. So does this mean that I'm not 8w pregnant that I'm only 7w? I'm so confused.