Charge Pipe Red

I was giving some people a ride home from a party last night when i got pulled over. I hadn't smoked anything that day, I didn't have weed or paraphanelia on my person The cop said my eyes looked red, and told me he pulled me over because my license plate light was out?? I went though a sobriety test and passed. The cops then searched my car, and found a bag of weed and a pipe. I told them that it probably was someone who just got in from the party that i was picking them up from. I got hauled down to the station, and was charged with ingestion, possesion less that 2 grams and paraphanelia. They made me take a piss test. What should i do? I had never even been pulled over before in my life, and my records clean. I m a student in college, and am on scholarship. The thing is, i didn't even know the pipe and weed were there. Please help