Did you have any ultrasounds before 12 weeks?
Babyboy, I wish I could give you reassurance. Your likely ovulation was March 8th 0r 9th (Feb 23 plus 13 or 14) which ties in with a due date of Nov 30th. On a standard cycle sex Mar 12th would have been too late to catch the egg. Nothing is writ in stone, but if you want to be sure then a paternity test will be in order.