I have a friend who likes to pose moral conundrums. Here is one that isn't entirely hypothetical:
Government officials call together all the adults of a small Cuban village. The officials announce that it is illegal to raise children as Catholics and that any practicing Catholic will have his children taken from him and raised as atheists by the State.
A villager, who happens to be raising his children in the Faith, is called forward and ordered to sign a document and swear that he is not a Christian and that there is no God.
What should the villager do?
The correct answer is, "He ought to refuse to sign and swear." (If you don't agree, ask yourself, "What would Peter do?")
And if the villager should sign and swear? Then he must confess his sin at the earliest opportunity.
Notice, though, that he can only confess his sin if he thinks it's a sin. If he thinks he was just dealt a lousy hand, he played it as best he could, and he'd play it the same way the next time, then what does he have to confess? What is he asking God to forgive?
The Sacrament of Penance and Reconciliation (as the Catechism inelegantly refers to it) requires three acts by the penitent: contrition, confession, and satisfaction. I suppose something like, "I don't see it that way myself, Father, but if you say it's a sin, I'll ask forgiveness for it," might be a sufficient confession, but there's not much in the way of contrition in it. The Council of Trent defined contrition as "a sorrow of mind and a detestation for sin committed with the purpose of not sinning in the future."
As for satisfaction, performing the assigned penance may expiate the particular sin, but it won't touch the disposition of soul that led to the sin to begin with, and that would lead to the sin again in similar circumstances. One purpose of the assigned penance is to "help configure us to Christ," and that requires a desire distinct from the desire that God forgive whatever sins He might be holding against us.
Conditional contrition, then -- "if this is a sin, then please forgive me" -- is a very dangerous attitude. It may be the best we can do right now, but the goal of the Christian is perfect contrition, sorrow for the sin because it offends God Who is to be loved above all else. We can't be satisfied leaving it up to the priest, or even to God, to determine whether our acts are sins; we ought to love God enough to want to know for ourselves ahead of time what is and is not sinful.
Moreover, we absolutely cannot plan to sin and then ask God for forgiveness. We might, again, be able to obtain forgiveness for the discrete sinful act, but not for the habitual disposition through which we sinned -- not that the disposition is unforgivable, but that we wouldn't be asking that it be forgiven.
Today is the time God has given us to pray for the graces to resist the tempations that might come tomorrow.