Wow. This is pretty fcuked up.
>> I did this right before I met my Fiancee so no cheating was involved.
Well in conservative cultures that is not true. But we are not gonna discuss American pre-marital behavior here.
(1) Have you done a simple blood-group and rhesus-type check? That is an quick way to eliminate mis-matches.
(2) Is there no lab that is ready and can do the DNA test in a day or two? Will the lady and her child agree to on short-notice? Do you need court's permission to do the test? Is there a way to sneak in and borrow hair/saliva samples of the child ;)
(3) Can't your lawyer or the judge understand the special circumstances and order the DNA test soon?
Disclosing such an issue after the marriage could be disastrous to you. My advice would be to disclose it before the marriage and deal with the consequences later.
Rhetorical question - Abortion (probably without the man's consent or knowledge) seems to be fine with this society but why does ruining a man's life after not being in contact for 3 years since conception seem fine?