You need to ask whether he ever really did redeem his actions. Shakespeare often deals with the theme of redemption and forgiveness, but in The Tempest it is very ambiguous. If any redemption on the part of Prospero is made, it is not unequivocal. His forgiveness is granted, but look at the reasons why.
He forgives most who wronged him prior to the opening of the play, but it is mainly as a result of the love he has for his daughter.