How to get rid of baby mama drama?

A little over a year ago I got a woman pregnant and didn't know until recently when she sent me a text asking for me to do a maternity test to see if it's mine because she isn't sure. I haven't replied but I want nothing to do with this woman or her child. I have a fiance that I love and adore and this situation would crush all I've worked for with her. I've been thinking about getting a lawyer before things get intense. I heard there is something I can try to get her to sign that would have her leave me alone and stop this from affecting my fiance and family. Please help