First Time Marijuana Offence in Georgia

My question involves criminal law for the state of: Georgia

Alright, so my friends and I were sitting in my parents car in one of my friends neighborhood. The cops pull up and there is smoke just pouring out of the car and we all freak out. So they walk up get us out of the car and search for the marijuana and I told them where it was. Also told them it was mine, they threatened us with jail time but ended just making our parents come pick us up because I'm 19 and still live with them. Made me pour out the pot onto the ground and stomp it. They never wrote me any sort of ticket but gave me a card so i could become an informant. Yet I'm definitely not going to be a "snitch." They were probably just trying to scare me into calling them because they said if I didn't then a warrant would go out for my arrest. Could they charge me for anything if they let me go with my parents if I do not want to be an informant for them? Seems like they have no true evidence of the marijuana and it would be like 5 days after the occurrence when they would talk to me about becoming one for them. What do i need to do?

Can they charge you with possession of marijuana after they catch you with marijuana and you confess to possession of marijuana? Is "Well, duh", still part of the teenage vernacular?