The mistake was a dent. Hiding it turned it into a total loss.

Most of the damage comes from the cover-up rather than from the original error. A mistake is a fact that can be fixed, absorbed and forgotten, and everybody produces a steady supply of them. Concealment converts it into a question about your character, which is far more expensive and lasts much longer. The repair also gets harder the longer it waits.

If something has gone wrong, say it early, say it in plain words, and bring your best idea for fixing it. Leave the explanation of why it happened until someone asks. People forgive errors far more readily than they forgive finding out late.