Baltimore Catechism:
Q. 780. What sins are we bound to confess?
A. We are bound to confess all our mortal sins, but it is well also to confess our venial sins.
Q. 781. Why is it well to confess also the venial sins we remember?
A. It is well to confess also the venial sins we remember:
1. Because it shows our hatred of all sin, and
2. Because it is sometimes difficult to determine just when a sin is venial and when mortal.
Q. 782. What should one do who has only venial sins to confess?
A. One who has only venial sins to confess should tell also some sin already confessed in his past life for which he knows he is truly sorry; because it is not easy to be truly sorry for slight sins and imperfections, and yet we must be sorry for the sins confessed that our confession may be valid – hence we add some past sin for which we are truly sorry to those for which we may not be sufficiently sorry.
Q. 783. Should a person stay from confession because he thinks he has no sin to confess ?
A. A person should not stay from confession because he thinks he has no sin to confess, for the Sacrament of Penance, besides forgiving sin, gives an increase of sanctifying grace, and of this we have always need, especially to resist temptation. The Saints, who were almost without imperfection, went to confession frequently.