An Office Problem - You Input is Requested (..and no I'm not involved)

My name is Nancy and here is my office problem. I have worked in my current job as an admin for two years. This was my first job after I completed my education and I started out here feeling eager to prove myself. I’ve done fairly well here and my performance reviews each year have been good. But recently I made a terrible mistake that has damaged my reputation, and I’m not sure what I can do about it.

I was alone in the office one lunch hour and went to a colleague’s cubicle to leave some paperwork on her desk. I noticed a file sitting in the middle of her desk and saw that the label read “salaries” and there was a stamp on the front of the file that read “confidential.” I have no explanation for what I did next, but I opened up the file and discovered it contained a list of staff salaries and proposed raises for each person.

I began to scan the list for my own name and, of course, saw what other people were being paid and what their raises would be. I didn’t spend long looking at it, but my bad luck was that my colleague’s manager came into the cubicle, saw what I was doing and grabbed the file out of my hands. He was very angry but merely said he would be reporting what I did to my manager.

Later in the day I got called into my manager’s office and was severely reprimanded. She said that she would be putting a letter in my human resources file documenting what I had done. If there are any further incidents of this nature, she said I would be fired. Needless to say, I also did not receive a salary increase.

Unfortunately, my colleague found out from her manager what had happened and now it seems everyone in the office knows. People have made some snide remarks to me and have called me “Nosy Nancy.” I’m no longer being invited out to lunch by colleagues and am generally being treated to a very cool and unwelcoming environment in the office. I realize I did something wrong but can’t help wondering why a confidential file was left on my colleague’s desk where anyone could look at it.

I’d really like to try and regain my good reputation but don’t know what to do. Do you have any advice for me?