First, I applaud you for your efforts to ensure the child you've raised is supported. To answer your question, some information is necessary. I will presume you and the child's mother were never married (otherwise you would not have signed the paternity acknowlegment). Did you register the paternity acknowledgment in the putative father registry? Also, was there a final determination of paternity?
Your remedies depend on a number of issues. Was the mother married to another man at the time the child was born or at anytime within the normal gestation period or if there is another legal father.
Legitimation can be a complex issue because it deals with procedures and perhaps various parties. As you can likely see, the DNA test results, exclusively, do not preclude you from establishing you as the legal father. I would suggest you contact a family lawyer to work through some of these issues and how you should proceed.
Best of luck!
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