Minor in Possession: MIP / MIC - What Are the Chances of Getting a Dismissal

My question involves criminal law for the state of: Washington.
I'm 18 and received a ticket for MIP/MIC. I was at a home where the police were called for a noise complaint. There were intoxicated minors present at the home, however they had partied elsewhere. There was no alcohol consumed and no alcohol found at the home by the police. They asked for my ID and kept it for nearly 2 hours. Everytime I asked if I could have my ID back, I was told to "..go sit down and wait. They weren't done with me yet." While I waited, the officers performed breathlyzer and field tests on 9+ minors. No field/breathlyzer test was performed on me. When my ID was finally returned, it was accompanied by an MIC/MIP ticket. At that point, I asked for a breathlyzer to challenge the ticket (I had not been drinking and had only been at this house approx. 10 min. before the police arrived), however I was told by the officers they needed to get going at that point and they were out supplies for the breathlyzer so couldn't perform one. I plan to plead not guilty, but what are my chances for a dismissal based solely on their police report and no physical evidence ? Also, should I get an attny to appear with me at the first court date listed on my ticket - and can my attny ask for a dismissal at that first hearing ? I'm not sure about the order of this process, I guess. Thanks for your advice.