A couple of things, Debora:
~If/when we have perfect contrition (not only “at death”), God forgives us thoroughly, we are told in Catholic theology. But as Church members, having received the sacraments of Initiation, our restoration to grace is imcomplete until we, as Church members, engage with that sacramental reconciliation to our Church, as opposed to a merely private reconciliation with God. And our Church is the source of an ongoing grace-filled life; otherwise, why be members of a Church? We might as well “create” our own separate religions, say our private prayers to God, trust in private personal graces. But that is very non-theological from a Catholic perspective, because Christ speaks, loves, gives, forgives, and teaches in community, through his Mystical Body, His Church. We experience the Trinity not only privately, but through Christ’s Church, his living Body. Jesus promised the apostles to send His Spirit to His Church, so when we ignore or bypass that Church, we try to ignore Jesus Himself.
~raaucoin has it right, that sin injures the ecclesial body. (Fr. Wade Menezes has often spoken of this on EWTN: Sin injures self, neighbor, Church, and cosmos.)
~It is a very classic Catholic theological concept that God forgives, rewards, and heals in anticipation of a completed act, after the heart extends itself to God with full intention to complete specific acts. That does not mean that the follow-through (in this case, the sacrament) is not essential, merely that God’s vision is magnanimous, and that his friendship/covenant with us is based on mutual trust, including His own, toward us. This was also operative among the Jewish people, in their history, prior to Christ’s earthly arrival.
~Forgiveness (the anticipation of it, the promise of it, the reality of it) is one thing; sacramental graces are something else; those are not available outside of the sacrament. Sacramental graces empower us to avoid those very sins which have been confessed.
~The genuine sign of one’s sorrow for sin is not private prayer but engaging with the sacrament of penance…just as the genuine sign of sorrow for offending someone else is not, by itself, an apology, but rather modified behavior, and often an outward act of restoration of that relationship. And we cannot effectively modify our behavior without the external benefits attributed to the sacrament; sacramental grace empowers us to change.