I respectfully disagree with your interpretation. That isn't how I read the Catechism. I read there that there is a very real and great divide between objective immorality, and sin. I read that in order for the eternal guilt of a moral offense, grave or otherwise, to impute to the moral offender, the offender must be acting in complete and total, unequivocal freedom and liberty when so offending. It is only during such a circumstance that a moral offense's guilt is imputed to the offender, and only then is that same moral offense sin.
The Church does teach to confess grave moral offenses regardless, however, which---and this is only my personal reading, understand---helps us when we are in particular spiritual trouble, which can manifest as our commission of grave moral errors.
No hard feelings.