SIns are specific. The only sin held against you is the one you’re hiding. The rest have been forgiven.
Being repentant is a state of the mind and soul. Purposefully ommiting the worst sin because it is embarrassing or hard will render the confession null. You are either reconciled with God or you are not. If you have a mortal sin on your soul you may as well have not confessed at all, since you are still guilty of mortal sin.
the man, my advise is this: I don’t know if this is true in your case or not, but many people have left the Catholic Church because they have this view that all Catholics do is follow the rules in order to be in communion with the Church. Pretty much a mindset of, task #1: confession, task #2: go to mass, task #3: tithe, task #4: receive the Eucharist. These people have missed the point all-together, confession is not just a necessary step so that you can get to your goal of being back in communion with God and the Church. Confession is THE most important step in gaining reconciliation with God. We are humans and in a constant fight with sin, reconciliation is the most beautiful gift God has given us, since it directly takes it’s power from the sacrifice Christ made for us. To go to confession is to tell God “I am human and I will sin, but I hate my sins because you hate evil, and I lay them ALL out before you.” To hold one back, is to hold yourself back from being reconciled. So, who cares one way or the other if all the sins you confessed are or are not forgiven if you entirely left the worst one out, you are still not reconciled with God, which is the purpose of confession.
If your problem simply comes down to being embarassed to say your “main” sin in front of a priest, we all struggle with this. But, our desire to do as God wills needs to overcome our desire to maintain our pride.
So, to summarize, I believe and have been told by my priest, that to have your checklist of sins and ticking them off as you confess them is missing the point of confession. For you to be frustrated because you have to reconfess all of your sins because you held one back is like being frustrated because you have to do a whole report in school over because you wrote it on the wrong topic all together. The frustration comes simply from a misunderstanding of the “project” at hand.