It sounds like you’re forgetting about God’s love.
He loves you, and He knows what sins you committed against Him. When you went to confession, intending to be reconciled to Him, you did what He wanted. If you forgot one particular instance of sin, or if the priest said he didn’t need specific details, THAT DOES NOT MATTER!!! God knows what you meant to confess, and you’re fine.
As for presumption, that particular sin lies in committing a sin BECAUSE you know God will forgive you if you later ask Him to. Committing a sin WHILE knowing (intellectually) that He will forgive you is not the same thing. It is only when you improperly commit a sin in reliance on being forgiven that you commit the (additional) sin of presumption. This is because forgiveness requires contrition, and – when you are actually guilty of the sin of presumption – you are incapable of feeling contrite (after all, if you did it on purpose, meaning to go through some meaningless ritual later, only to then commit the sin again, you aren’t contrite, are you?).
In other words, I doubt that you are guilty of presumption. In my view, the mere fact that you feel contrition is evidence of a lack of presumption – because people guilty of presumption, by definition, don’t feel contrite. I think the only problem here is scrupulosity – in your case, viewing God too legalistically, worrying that He will seize the opportunity to say “Gotcha! You’re going to Hell!” because you forgot to dot an “i” or cross a “t” when in fact we know from the Bible that the opposite is true: He will seize every opportunity to welcome you into Heaven.
The Sacrament of Reconciliation is a gift from Jesus, who is God’s Word. It is not a trap for the unwary, or the careless, or the ignorant. You went; you were absolved. The priest is granted that power by God, and the power is independent of the priest’s personal moral character. If he absolved you, you are absolved. Period. No “But I wasn’t specific enough;” no “Oops! I left one out;” no “Gosh, do you think I could have broken that one sinful incident down into two separate sins instead of confessing it as one sin.”
Jesus didn’t go through the Incarnation, the Passion, the Crucifixion, and the Resurrection just to condemn you for obeying your priest’s instruction during a Sacrament. You confessed; you were absolved. God loves you; so do we.
You come out as clean has a new born babe after baptism, and that my friend is the beauty of Christ’s “full” gift to His Church, [unavailable in other religions, but available nonetheless to anyone baptized Christian if they desire to come with sincerity to confess to a Catholic priest].