Minor in Posession Alcohol & Drugs: MIP, MIC, Intoxication

In Texas last year when I was 19, I was riding with a friend who had afew beers (unopened) in his backseat. We were pulled over because he was speeding (so the cop says). He walked up to the car shining his flashlight and saw the beer and told my friend to get out of the car. He was given sobriety tests and told to sit on the police car. One of the cops (now there were 2 of them) told me to get out of the car. He searched the car and came back and put my friend in handcuffs and put him in the car. He then proceeded to give me 2 sobriety tests which I passed, he ran my license and it came back clean. Then to my surprise, he told me to turn around and put my hands behind my back, that I was under arrest for "posession of alcohol" (his exact words). I was in jail for approx. 11 hours. I bonded out and got a lawyer for $150, my plea bargain has already come through which is $175, 8 hours community service, and an alcohol awareness class. This is my first offense, and my first time in jail, which I think jail is obsurd for an MIP. I don't want to take the plea bargain, but I also don't want to dish out the money for fighting the ticket. What should I do?