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

I merged for the right lane to the next lane to the left when the right lane becomes an exit only lane. There is a sign the says "right lame must exit". I merged to the left before the lane line become solid but after the must exit sign.

The officer told me that it is not a lane violation but failurt to obey traffic sign. Am I at fault merging to the left eventhough i did not cross a solid line?

Thank you