I known her for 23 days and she said she was 21 days prego when she did the test at 19 days of knowing her?

Lol, okay do the math, a woman ovulates 2 weeks before she starts her period, which means that an egg is released from the ovary and passes through the fallopian tube into the uterus waiting to be fertilized, so when you had sex with her, she either a)had ovulated that day or b)ovulated a few days later, meaning that your sperm reached the egg and fertilized the egg and she got pregnant. So that means that YOU are the father of this child. When she says she is 3 weeks pregnant, it means that it is 3 weeks after her last period, so if you want to get technical, she really has only been pregnant for 1 week, but doctors go by the last menstrual cycle a woman has had, maknig her 3 weeks pregnant. So yes, you are the father of the baby!! It just turns out that luck wasn't on your side, and you had sex with her on a day that she was ovulating! Should wrapped it up, bud!