You have the right to fight the charge, attempt to convince the juvenile court that you didn't know that anybody in the vehicle had marijuana, and see what the court decides.

You were a passenger in the car, not the driver or owner, so you don't have standing to object to a search that may have infringed the rights of the driver or owner. Further, if the police officers justify a search based upon "plain smell", specifically the smell of marijuana, and then find marijuana, it's an uphill battle to try to convince a court that the officers did not in fact smell marijuana. If you're a smoker you may not be sensitive to the smell, or how it clings to cars and clothes; officers are sensitive to the smell.