Wrong due date???

Briana • mama to a sweet baby boy 💙

So according to my last period I should be due May 23rd, however I have very irregular cycles and so my OB scheduled a dating ultrasound. I started experiencing pregnancy symptoms the weekend of Sept 30th and got my bfp on Sept 30. My dating ultrasound says I'm only seven weeks along, which would've meant I got a bfp while only 3 weeks pregnant. Is that even possible or is my dating ultrasound wrong about how far along I am?