Ay, common yan mama, lalo na kung mabilis lumaki ang baby mo! A few of us went through the same thing, ang ultrasound dating based sa size ay mas accurate especially pag mas advanced ang pregnancy, kaya yung Sept 1 ay possible talaga depende kung paano siya nag-develop. Best to discuss with your OB which date siya mas confident about kasi may factors din like if you had irregular periods or late ovulation, pero honestly, baby will come when baby is ready, hehe! Just make sure everything else sa ultrasound looks good at follow-up lang ang advice ng doctor mo.