Well, first step is to calm down. In the end, you weren’t the reason it was there in the first place so you don’t have anything to worry about. If I were you I’d return to the spot you found it and call the authorities to get them on the scene. Don’t put it back where you found it, just explain to the officers the situation. Shit happens, probably not the first time someone has moved something from a scene like this. The only reason I wouldn’t put it back in the place you remember it is because if there’s any other clues there to show how it got there in the first place, you don’t want to destroy any other evidence.

Shits crazy bro, but best of luck. My sympathies are with you