Keep the car, per metro.net travel planner and Google Maps, it would take you, for example, 2.5 hours each way from the Queen Mary to Santa Monica Pier for example, taking 3 separate conveyances. I have stayed on the Queen Mary a couple of times and there is not enough to do in Long Beach to occupy 2 days.

>>there is not enough to do in Long Beach to occupy 2 days.<<

>>the aquarium, Shoreline Village, whale watching trip and/or a day trip to Catalina<<

However -- even w/ all that I'd also keep the car and return it at LAX. You'd have a lot more flexibility.