Internal Possession in Pennsylvania

My question involves criminal law for the state of: Pennsylvania

at age 17 i had nothing to do so i went over a friends house and they were drinking. i didn't drink because i had to drive home. cops raided the house and breathalyzed us. i was the only one that blew a 0.00%. the cops said I'm still getting a citation for underage drinking and i didn't understand why. I literally didn't even have a drop of alcohol. then i read up on it and found out about Internal Possession. what should i do in court about this? should i plead not guilty, and what are the consequences of Internal Possession?

As long as you were near enough to the alcohol to have some if you wished, you were close enough for possession.