You should inform the parties in concern about your mistake. It will reflect badly on you, if someone else discovers it. Worst yet, if someone else tells the parties in concern.
2. Deny that it ever happened (/Cover up the mistake)
You may fear that the response might be loss of status, ridicule, humiliation etc. Yet, even the most cursory study of political and corporate cover-ups in recent years will show, concealment uncovered inevitably does more damage than the original error.
3. Not taking steps to “fix” or alleviate the effects of the mistake
You accidentally deleted several important records from the database.
When you go to your boss to confess your mistake, have a plan on how you can correct it. Are there backups, what alternative measures can be taken etc
Of course, depending on the extent of the mistake there may be very little you can do to rectify it. Often, showing true remorse with a humble apology goes a long way.
4. Blame factors outside your control
There may be relevant contributory factors such as the long hours you have been working or the fact that you didn’t receive some information you needed, and it may be relevant to mention these, but don’t use them as pillars to hide behind.
5. Attack other people for their mistakes
More common with siblings at young age! Some, never seem to grow out of it!
6. Beating yourself up over the mistake
The fact that you made a mistake does not negate all the accomplishments and successes you have achieved. Don’t drag yourself down by constantly going over and over the mistake. Obsessing can’t undo the mistake or rectify it. Resolve never to make that mistake again and move on.
7. Not learning from the mistake
Carefully evaluate why you made the mistake? What can you learn from it? A mistake has value only if you learn from it.
8. Not taking measures to ensure it doesn’t happen again
What can be done to prevent the mistake from happening again?
it won't and i want you to believe me.. the different between mine and yours is, i can't fix it.. its all been done, and if i keep regretting it, which i did before, there will be no "us". I'm just trying to move on and live my life as normal as i can. but with you mentioning it, over and over again is just bringing me down.