How do I expunge a misdemeanor?

I was working for a tow company and had a sheriff’s call. When I got to yard to drop vehicle, there was an enormous amount of garbage and stolen things in truck. Hundreds of things. When moving the truck, I saw a little pouch with foreign money in it and thought I would put in the office so when owner comes it will have been safe. I thought I have put back in truck but it was with the paperwork I got from sheriff to tow vehicle. Long story short, I had the pouch with me and I was on another call. I did not realize I even had the pouch until they called our office asking If I had seen pouch. Of course, I told them yes and that was that. Well, I ended up being on the other call for over an hour and half in mountains. When I got back to yard, the sheriff was waiting for me and was pissed they had to wait and that I had the pouch. I got scared because I had never been in trouble with the law ever. He ended up writing me a ticket for petty theft and I had to pay a fine. I didn’t take anything in the first place and never intended to plus it was foreign money. I have already paid my fine and have about a year on probation but I need this expunged as soon as possible. Its keeping me from getting another job. Its already killed me getting a few really good positions with major companies. I need it off. What can I do?