|Presumably, you have already taken step one...return the stapler. If you did not have a real discussion of what happened in the car on the way to the meeting, you should do so now.|
When you make a mistake, the best approach is to admit it, apologize, and correct it. People make all sorts of mistakes in their careers, some large and some small. In many cases, the mistakes may be excusable if the person who committed them is honest and forthright about what happened. What tends to be inexcusable is when the mistakes are repeated.
Once you have given your mea culpa to your manager, you need to move on from this point. If you keep returning to the issue, it will never move from the foreground into the background. Let your manager see that the incident was an aberration, and let your performance clearly demonstrate your work ethic, drive, skills, and honesty.
You made a mistake, suffered some consequences, and hopefully learned from the ordeal. The only other suggestion is to buy your own stapler.