1765 Sanctum

A Rule of Peace

For a man who struggles with scruples, to follow with his confessor's guidance. It never excuses leaving out a mortal sin you know you committed (CCC 1456).

Choose one confessor and make him your regular confessor. Tell him you struggle with scruples.
Confess on a set schedule — not whenever the anxiety spikes. Let the calendar, not the scruple, set the pace.
Never re-confess an absolved sin. If it is already forgiven, it is forgiven.
When in doubt, assume no sin — and act against the doubt — unless your confessor tells you otherwise.
End each examination with mercy, not with checking. Make a simple, honest examination of conscience, then stop, and entrust the rest to God who is greater than your heart (cf. 1 John 3:20).

What the Church requires for mortal sin

"Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent."
Catechism of the Catholic Church, 1857

All three, together:

Grave matter — the act itself must be seriously wrong, not a small fault.
Full knowledge — you must know, in the moment, that it is gravely sinful and against God's law.
Deliberate consent — your will must choose it freely and on purpose.

This is formation, not clinical or medical advice. It cannot diagnose you and is not a substitute for the counsel of your own confessor or a qualified professional, or, if scrupulosity is severe, a Catholic-friendly mental-health professional.

From 1765sanctumco.com/catholic-scrupulosity/

Excerpts from the English translation of the Catechism of the Catholic Church for use in the United States of America Copyright © 1994, United States Catholic Conference, Inc. -- Libreria Editrice Vaticana. Used with Permission. English translation of the Catechism of the Catholic Church: Modifications from the Editio Typica copyright © 1997, United States Conference of Catholic Bishops—Libreria Editrice Vaticana.