Confuse sa EDD

Hi everyone. First time preggy po and currently on my 39weeks,3days. Kanina lang nagpaultrasound ako na pinarequired ni OB. 3times sinukat size ni baby and it shows EDD is Sept.16,2020 hindi Sept.2 na ineexpect nmn lahat. Regular naman ako mg mens and tanda ko pa ung last mens ko. Alin po ung dpat sundin dto, mas accurate po ba ang ultrasound? #advicepls #firstbaby