To be honest man up and take on your responsibility that will soon come. From all that u said and what Brooke is saying u seem to be 100 percent the father. No need to try and find fault to get your self out of this.
But again, what does she need to confess? If what you are suspecting (that she had gotten pregnant before the two of you became intimate) is true, she is not pregnant now and she has not been intimate with anyone else since meeting you, so why are you saying you require her to "confess"? That is a word used when someone has committed a crime. She might (and I still stress you don't have proof) have been intimate with someone else before she met you. That is a crime?
Here is a link to a site that can explain that the first two weeks of the time a doctor allots to pregnancy are actually before you get pregnant.
http://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-care/art-20045302
Hi, scorpion, did the doctor say that "the embryo is six weeks old" or did he say the pregnancy was six weeks along? Doctors usually measure from the first day of your last period, not from the day of conception. Did you say to the doctor "Does that mean the baby was conceived 6 weeks ago?" and the doctor said yes? Or did he just use words like gestational age and a number of weeks "along?" What due date did the doctor give you?