[quote="Edmundus1581, post:8, topic:290659"]
There are two reasons I can't answer this: first, you are unsure whether it was mortal or venial, and, secondly, you are asking whether you "should not" confess it next time, which is different from asking whether you "should". :)
What I have done in similar situations is, in the confessional, mention why I think I might need to confess something that was left over from a previous confession, and then follow the priest's advice. Each time he has said said "You don't have to confess it, but if it will ease your mind then go ahead". (Note, I'm talking about doubtful cases here, not the clear ones of a a forgotten mortal sin).
So, if this were me, I'd say "I forgot to confess something in my last confession. I'm 95% sure it wasn't mortal", and hand it over to the priest. :)
Then I would get the peace of mind of knowing that I've handed it to the priest, and I also get the benefit of his advice for future reference.
In 30 years as a Catholic I've only asked three times, because each time I've learned so much that I don't need to ask again for many years. There have also been three occasions where I've confessed forgotten mortal sins, without asking, because there was no doubt about the need to confess.
Thank you :) I'll hand it over to the priest next time :)