My question involves an injury that occurred in the state of: California

If the lanes are numbered from left to right: 1-4

I was in the number 4 lane and merged left into the number 3 lane as traffic was slowing. I did the look over your shoulder, check mirror, and use turn signal as per law.

I had enough room to get into the lane and come to a complete stop with traffic before I was struck by a car merging from the number 2 lane into the number 3 lane which I didn't see because... well... he wasn't in the lane I was merging into.

his front right bumper struck my rear left bumper and pushed me into the truck in front of me.

Will I be found at fault because we were both merging? Or, am I considered established in the lane because I was in front and managed to stop before being hit?

Thanks