Thanks for your query.
If your periods are regular every 28-33 days ovulation day is expected to happen D11-D21 counting from the first day of the LMP.
This is called fertile time because intercourse during this time increase the chance of pregnancy
If your gestational age
was 11 weeks +6 days on sept. 19th , chances for you to have remained pregnant is at the beginning of a month .
The chance for being father the latter is very very low.
Take care of your self