If I'm on the birth certicate and raised the child for 8 months but just recently found out that I'm not the biological father, do I still have parental rights?

If you are on the birth certificate, you are considered the "presumed father" father of the child with all the rights and duties of a parent.  If a custody suit is filed that determines you are not the father, then, unfortunately, you will no longer have any parental rights to the child.  If neither the mother nor the father step up to the plate to be mom or dad, then you would potentially have standing to file for custody of the child.  If one or both parents decide to assert their rights and they are otherwise fit to be a parent, then their rights will control over your history with the child.