Open the trunk, somewhere stamped along the gasket rail is another vin number, see if it matches. CHP can and does take the car if a certain number of vins do not match out of the total. You will not get it back.
I would do your homework, all of it, don't take any shortcuts. Put it on a trailer (if not stolen) and take it somewhere else and get title. If you bring it back to California after being titled, they will assess an import fee. Las time I dealt with it, it was $400. That might have changed, but get it out of California. They are nuts down there and its spreading.