Once someone becomes a Christian, they must ask forgiveness of their sins and God will forgive them.
Acts 2:38 says that baptism is "for the remission of sins". Can you become a Christian before your sins are remitted?
Acts 22:16 says that baptism "washes away sins". Can you become a Christian before your sins are washed away?
Galatians 3:27 says that "as many of you as were baptized into Christ have put on Christ". Can you become a Christian before you "put on Christ"?