whos the dad?

So I'm really iffy about posting on here but I constantly worry about this all the time. On October 16 I had an incident at college involving alcohol and a jerk of a guy. I found out I was pregnant on November 29th and the doctors said I concieved on November 5th. I am currently with my fiance and mostly believe that he is the father but the pregnancy came as a shock to both if us due to the fact he has said that he cannot have kids. I know there isn't much of a chance that it could be the guy from the college (which I am currently not attending the same one anymore) but I cannot help but think of what if. What if the doctors got the date of conception wrong? I'm terrified if what I'm going to do if it's not my fiance's (he knows about the incident) so I guess I'm just wondering what you guys think? Do you think it's my fiances or no?