Before thinking of nikah both of you need to repent and ask forgiveness of Allah for the grave sin you have committed. Once you have done that, you may get married; but you should do so legally and Islamically; it has to be proper marriage with all of the requisite conditions. There is no harm, however, in renewing the contract for the benefit of your parents.
By performing a valid marriage you are covering yoursels and providing a father figure for the child out of wedlock.
For further details, please consult the following answers: