MIP in CA

I was charged with a minor in possession of alcohol on may 19, in CA. This was on a college campus during a yearly campus celebration. The office simply stopped me, asked if i knew that alcohol was not allowed on campus, and opened up a large red plastic water bottle (the kind that hikers often carry) I was carrying that contained coke and rum. This was with out asking permission for a search. Also on my ticket it states that this an infraction. I was wondering what my options are considering that if I admit to the charge I would lose my driver's license for a year.

ps Would the lack of asking permission to open my water bottle constitute an illegal search?

Not if he smelled the alcohol on your breath and you were seen drinking from the water bottle or he smelled it coming from the water bottle.