If you sign a legal doent saying you don't want child support can you change your mind.?

I pay my child support on time like I am supposed to and my Ex-Girlfriend does not want me to be apart of my daughters life.She gives me trouble every time I try and pick my daughter up and it is just to much she calls the cops and tells them stories and it has gotten to be to much.Well she calls and she agrees to stop the child support and the back child support if I sign over my rights .She has also agreed to sign papers and have them notarized stating that she don't wont anything from me if I sign over my rights .What do you think I should do ?