If he didn't know he wasn't the father?
Or if he knew he wasn't the father?

Yes he will, in some states, depending on how long he was on the birth certificate he is just stuck on it and will be the legal father even if not the bio father. In other states, he can challenge it, ask for a DNA test and ask to be removed.

But as long has he is still on the birth certificate he will have to pay child support

Get a lawyer, immediately.

OK the mother told me after 2 days that I would not sign the paper that if I did't sign the paper I or my sick dad could't see tha baby and that would have heart him so in other words I was forced.

Depends on where you live. You could be considered the putative father and be ordered to pay child support. You should get an attorney and demand paternity testing.