please help so confused on ultrasound

Christina
So on nov 29 I went An got my first ulterior sound I was 6w and 0 days. So I counted back 6 weeks it put me at October 25th but why are people saying I didn't conceive until nov 1st? If I was 6 weeks on nov 29th I thought that ment I would f had to conceive a little before October 25th.