Minor in possession of marijuana in Mississippi help.?

A week or two ago I was charged with possession of marijuana and I am a minor. My mother went to justice court and they ladies there said that they could also get me on DUI although I wasn't charged with that at the time. The truck that the joint was found in was also not mine. My friends and I were sitting on the tailgate of the truck that the joint was found in. What kind of sentence would I be looking at? Is there anyway to get out of this because it wasn't my vehicle?