If you conceived from sex October 9, the baby would be wildly overdue by now, like you'd be in your 44th week of pregnancy.
No, you're fine. Guy A is three or even four weeks too early to be the dad.
Even if you were to have the baby early, it wouldn't mean the baby was conceived at a different date than the ultrasounds have indicated. Babies do sometimes come early, after all. That doesn't reach back in time and change when they were started.
In fact, if you had gotten pregnant by Guy A, you would have had the baby by now. Due date for a baby produced by sex October 9 is around the 4th of July.
Congratulations on your new little one. :-)