PARDON AND PEACE: BOGEYS
From Pardon & Peace by Fr Alfred Wilson
"There is no obligation to confess doubtful sins. The catechism for the Diocese of Rome, approved by Pope Pius X, has this question: “If a person is not sure of having committed a sin, must he confess it?”
And the answer is: “If a person is not sure of having committed a sin, he is not obliged to confess it; but if he wishes to, he must add that he is not sure of having committed it.”
The Council of Trent tells us that we are bound to confess all mortal sins of which we are conscious. In this case you are conscious, not of sin, but of a doubt about sin; and you cannot simultaneously be conscious of doubt about sin and of sin, any more than you can be conscious simultaneously of certainty and uncertainty in the same matter.
Common sense tells us that a doubt cannot create a certain obligation, any more than uncertainty can, of itself, produce certainty. If there were an obligation to confess every sin of which we are not quite certain, Confession would become a bugbear, especially to people with a bad memory. Doubts are, therefore, matter for solution rather than absolution, and are to be solved not absolved.
Many people will be inclined to object to this: “Yes, that’s all very well in theory, but in practice, is it not far better to tell doubtful sins? In fact, would it not be unwise to omit them?”
It all depends. If very occasionally you remember such sins and do not make a habit of it, nor “get in a state” about it, then it is better to confess them just as they are, and have done with them. But if, on the other hand, you do make a habit of it and are constantly afraid of having omitted sins, then it is far better not to confess. "
Apologetics and Catholic Doctrine by Archbishop Michael Sheehan
“( C ) A doubtful sin is one as to which there is uncertainty in regard to its commission or its gravity or whether it was previously confessed. If the doubt is supported by good reason, confession is not obligatory, though for the penitent’s peace of conscience it is usually advisable.”