Drunk in public, how could this be?

Before I begin, I am in Virginia and of legal age to drink. I went out to the bar with 4 of my friends and I personally had 2 beers. I drove up to the bar but being that my record is spotless and I am trying to work for the federal government, I choose that I wasnt going to drive and catch a ride with one of my friends. I have jumped in the back seat of my friends car and headed up to the gas station. The driver went in and out and got a few small things. All of the sudden there are 3 police cars that pulled up accusing her of cutting a police officer off. I am a pretty big guy and I am fully aware of my sorrounding after two beers, I did not see any police officers. We were very curtious and answered everything we were asked. When we left the bar the driver seemed perfectly fine and I was ured that she was fine to drive. They breathelized her and she blew .085 which is just a little above the legal limit. They gave her a drunk in public but then they got the rest of us out of the car. At first senior officer was going to allow us to catch a cab but choose to have the decision to be made by a junior officer (21yo, we found out later). He choose to arrest all of us for drunk in public. Yes, I had two beers but none of us besides the driver were breathelized, we were just simply arrested without any further notice. We were not being loud at the gas station or caused any trouble. We were all charged with a very minor misdemeanor that is pre-payable and the worst possible punishment is $100 plus court costs but it is still a misdemeanor and I would like to fight it, I am not concerned with finance but rather having this charge dismissed. How could they have done this in the first place. I have no priors and was just trying to be responsible by not driving even though I was way under the limit. We were thrown in the "drunk tank" pretty much sober and released the same day without any trouble but how could they have charged us with this? How can I fight this, there was no way for them to prove that I even drank besides the fact that they "smelled alcohol" on us.