Hi Jacob,
If you had sex in October and her last period was in November, you are NOT the father.
For her period on September 22, her next would have been due around October 20 (corresponds with you said she was 3 weeks late on Nov. 8). It would be very unlikely that she would get pregnant having sex within about 10 days BEFORE her period was due to start until about 6 days AFTER.
Her next period after October 20 would likely have been around November 17. The November 8 date, does not appear to have fallen within when an expected period would occur.
I don't believe you are the father but only a DNA test can confirm. It can be done NOW, using her blood and a sample from you. Look up "non-invasive DNA testing." It's expensive.
Define "late."
Most women run about a 28 day cycle. Day 1 is when their period starts. They will normally ovulate between about days 11 - 16. The egg only remains viable for about 48 hours, after that it can't be fertilized. Sperm can survive up to about 5 days.
After about day 18 of their cycle it is too late for them to get pregnant and their fertility is decreasing rapidly.
Nothing is "concrete" when it comes to biology, timing can vary. Is it possible, yes. Is it likely, no.
Women can have spotting and/or bleeding early in pregnancy, it's very common. It can happen at any time and often can appear as a light period.
Conception can't be delayed more than about 48 hours after ovulation. After that the egg is dead. Your sperm can only survive up to about 5 days - maximum. The vagina is hostile to semen.