My question involves a traffic ticket from the state of: CA

I was driving on a 10-lane freeway one evening and decided to change lane since I was close to the exit. Since I drive a full-size pickup and it was dark outside, I was extra cautious. My blinker was on and I changed lane while observing for any car in my blind spot. A police office pulled me over and issued me a ticket for 21658(A) unsafe lane change. Does anyone know how to contest this ticket or whether I am completely at fault for taking caution in a lane change.

Thanks.