I knew nothing about the drug nor its existence in the truck, what do I do?

Got pulled over in my uncles truck for expired tags. Officer came up asked for my insurance, I couldn't find it so he went back to his car. He then came back to the truck and asked why the truck smelled like weed, I then told him I smoked before I left home. The officer then asked if he searched the car would he find anything illegal. I then told him where the "roach" was and he had me stand Infrint of his car while he searched the truck. After searching the truck he then approached me with a black bag that had needles, a spoon, and a bag with a dirty diamond like rock. He asked me if I knew what it was and I told him no asked to look at my arms and didn't see anything that showed I'm a user of whatever the drug is. Arrested me and charged me with possession of controlled substance under1g