I just found out that I have a 12 year old daughter. I have asked a number of times over the last 13 years if she was mine and told no. The mother got married when she was pregnant and he thought the child was his until now. I have met the girl and I am willing to do anything for her. Do I have any rights?

Well depend on the state ( assuming you live in the US, since we have people here from 100's of nations)

In some states if the daughter was born when she was married, and the other man was listed on the birth certificate, actually in some states you may not have a right to require a DNA test and contest the birth certificate.

If you live in staes where it is allowed ( which is most) you will first have to file in court for a DNA test, and then file for visitation rights.
Of course there will be a child support issue, which may include back support.

Yes I live in Az and the girl in NY. The mom voluntarily told me that the girl is mine. We have done a dna test not a legally binding one, but I am a 15 of 15 match. The husband has made several legal threats to the mother and myself.

So he made some legal threats, so what, if you are the actual father there is nothing legal he can do. So laugh at him basically. Who cares what he things, that is an issue between him and her, as for as divorce or paying back child suppoprt if he was paying it.

For you, it is your choice now, if you want, you have to file in court for a real DNA test that is binding in court. Then you file for visit rights.
All that is needed now is lawyers and court.

You need a lawyer. A child is not a television. If the mother was married at the time the child was born, then her husband may well be the legal father until the matter is cleared up by a lawsuit. Also, what does the birth certificate say? You need to get one, if at all possible.

He is on the certificate. I am not sure if they were married before she was born, I am not looking to go to court and get joint custody but trying to find out what can happen. Her mom already said she can come visit and what not. I will also travel out there again to see her. I appreciate all the info

You need a lawyer. The legal relation of father and child is not created by private agreement. At some point the fact of your paternity needs to be proved, and it should be done ASAP, while everyone is in agreement.