['Yesterday I did something at work that I am not too proud of. I went in my coworkers desk and took some supplies. Now, it is eating me up inside.']
I bet you felt guilty about it afterwards. Just let them know you needed it really bad at the moment and maybe return it?
Yesterday I did something at work that I am not too proud of.  I went in my coworkers desk and took some supplies.  Now, it is eating me up inside..