I see properly placing the boat on the cradle as being the marina's responsibility.
Well, yeah, but how is "properly placing the boat on her cradle" defined? The marina might argue that you provided a cradle that one might reasonably
assume was built to fit the boat without blocking up the keel with additional materials. (Some of the cradles for some of the boats in our sail club need such shims, some do not.)
One assumes you signed some sort of paperwork with verbiage relating to their responsibilities and liabilities. Read it carefully before approaching them.
However, in the end: You're the skipper. It's your
responsibility to see to the health and welfare of your boat. IMO you should have checked her immediately following haul-out.