I had sexual intercourse with this guy back on July 23 2011 and got pregnant and my due date was April 12 2012 I had her on April 13 2012 is it even possible for him to be the father?

Yes, it's possible. The nine months start with the beginning of your cycle, not the date of conception. And, it's not exact - some people deliver early, some late. Calculations for due dates are approximated as well - the reason most people do not deliver on their actual due date.