You have been cited under § 2.04 of the Public Courtesy Code: Unreduced Backpack Profile
TAKE THE BACKPACK OFF.
In a crowded car your backpack doubles your footprint at exactly the chest height of everyone behind you. Every time you turn, you clear a radius. Take it off. Hold it low. There have been posters about this for decades.
This is not a fine. There is no fine. Think about what you did.