Minor in Possession, in California

My question involves criminal law for the state of: California
A few months back i was taken to a party with a couple of friends of mine. I was sitting in the backyard talking to a group of girls when the cops came into the backyard and said the party was over. They asked everyone theyre age and if theyd been drinking. When i replied I was 18 they took me out to their cars where they proceeded to breathalize me. I blew a .05 and was charged with a minor in posession. When the cops showed up I had no alcohol on or around me. I was the only person that was breathalyzed out of everyone at the party. I feel i was wrongfully charged am I wrong in thinking so?

Why do you feel you were wrongfully charged?