disobeying officer

Maryland. Following a baseball game I was turning onto a 2 lane (each way) road that leads to a major city outside of Baltimore. Cars ahead of me were turning, but when I got to the intersection, the officer waved me straight (there was no emergency or traffic jam). I stopped to ask why and state that I needed to get on the highway. There was no apparent reason for her decision and she refused to tell me why. She then told me to pull over and gave me a $275 ticket for willfully disobeying a lawful order and direction of a police officer. At the time (and even now) her actions seemed so random that I just didn't understand. After I pulled over to the side, other cars continued onto the road and there was no back-up or difficulty. I want to challenge the ticket, but I'm not sure how to proceed. I would appreciate any suggestions.

[JETX]

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