A few years back, while still an undergraduate student, I wrote and submitted a paper to a (low-tier) journal. It was accepted and published. None of the professors in my college were familiar with the subfield in question, so I did it all on my own, without their supervision or assistance.
It was only later on that I realised that I was guilty of plagiarism. I did write the paper all on my own, and always provide appropriate citations, but sometimes I would quote single sentences or parts of them directly from my sources without indicating that they were direct quotes (even if these unmarked quotes were always followed by a citation to the original source).
It has now been several years but I keep feeling guilty about it, and worry that one day someone will notice it and call me out on it. Or at least notice it while reading the paper and think worse of me. But since it has been several years since the paper was published, I also don’t know what I could do about it. I have thought of putting something like a public admission and apology on my website (from which the paper can also be downloaded), but maybe I’m overthinking it and nobody would actually care. In that case it would feel like a bad idea to needlessly draw attention to something that nobody would have noticed otherwise. But the paper has been cited some times, and I have reason to expect that there will be people reading it in the future.
Should I do something about it or just let it be?