Why do I apologize for work I finished on time?

You hand in good work on time, then immediately point out what you would have fixed with more time. You apologize for the finished thing instead of just presenting it. The work is fine, better than fine, but you hand it over already half-taking it back. Notice what that habit does. It teaches everyone to see the flaws before they see the work, and it teaches you that nothing you do is quite enough. But done and on time is not a lesser version of the work. It is the work. The imagined perfect version does not exist and never gets delivered. Next time, hand it over clean. Say, here it is, and stop. No note about what could be better, unless someone actually asks. Let the finished thing stand as finished. It is allowed to simply be good, and so are you.