Explain the reasons behind your course of action. If you tried to fix a mistake before bringing it to the attention of your superiors, explain why. Was it simpler and less exhaustive for you to fix the mistake yourself rather than distract others from the important matters they were dealing with? Or, if you brought the mistake to the attention of your superiors before resolving it on your own, it should be for reasons such as a superior being able to resolve the matter in minutes as opposed to costing more time and payroll hours for you to fix it on your own.

"I spent several days implementing some new systems to increase the quantity of my work. When I first put the system into practice, I was overly eager to turn my work in. I should've been more thorough in reviewing my work and not taken my new systems for granted. I met the deadline, but my work was barely acceptable. I pride myself on always padding the job, and turning in the finest quality. This work didn't meet my standard. I shouldn't have rushed the work and should have given myself a little more breathing room. I've since fine-tuned my systems, and am providing a higher output of material that meets my quality standards. Live and learn."