Get used to it,,, at your age you will start forgetting all kinds of things.

Go back to the local Sheriff's Department. File a lost property report and provide the make model serial number. If you have these bits of information and report it, the weapon has to be entered into TCIC/NCIC. This will do good things for you. Number one it creates a record for you. If the weapon is ever used for illegal activity, you have a case number on file that indicates you were not in possession of the firearm. Two, if the gun is ever sold in an instance where FFL rules are to be followed, the Sheriff's Department will get notification and you get your gun back. If a cop runs the serial number, again the Sheriff's office will get notified and you get your gun back. If you don't live in that county, you can probably do the report over the telephone.

Report the serial number to the police. If it is taken to a pawn shop it will pop up on the police data base that is linked to all pawn shops.

I did the exact same thing at Lake Aquilla a few years ago. We are human, and we all make mistakes. Don't beat yourself up to badly. It may take a little bit of time and sacrifice of other purchases, but it can be replaced. If you have a home owners or renters policy you can file a claim with your insurance company since it was stolen. Put an ad on Facebook market place and on Craigslist. I would also put an ad in the classified section of the closest towns newspaper. Find the nearest convenient store and ask the clerk if anybody has come in boasting about finding a gun.
Whoever picked it up most likely told several people, so someone is bound to see your ads.