You are overthinking this.
When you have been away from confession for years, the priest does not expect you to remember the number of times you committed each sin. I was away from confession for 18 years, and for some years before that I probably made confessions that were incomplete because I had doubts about something actually being a sin or some other confusion going on. I did not go into the confessional with the thought, “I just won’t mention this sin or that sin”, rather I was confused as to what I should be confessing and what I should be doing in life in general. I realize this sounds like the height of idiocy but I was in my 20s, we didn’t have Catholic Answers or an Internet, and I probably had some blinders on as to my own behavior because I didn’t want to think of myself as being a bad sinner.
Given all this, I could worry about all those past confessions and past years with lack of confessions, but I just confessed all the big sins I could remember, said I was sorry for everything and that was that. A few sins I forgot or still had some confusion about popped up on later confessions and I made sure to go confess them. From time to time I remember something from way far back (like 1989 or 1999 etc) and if it really bugs me I just mention it in Confession to make sure, but 99 percent of the stuff I confess now is recent stuff. I go to Confession about twice a month so I keep up with everything.
From what you have described, your past confessions were made in good faith, you didn’t willfully withhold any sins and you should be fine.
If you forgot something - and by that I mean you qualitatively forgot a grave sin, rather than worrying about “number of times” or a small sin - then you can mention it in your next confession. You do not have to re-confess all your old sins because you forgot something.