O. scyllarus can be picky eaters and often stick with one item. It can take days or even weeks to get them to switch diets. When given food that is easy to open like clams or raw shrimp, that's what they will chose. At this point, unless there is a physical problem with the raptorial appendages, the animal should be able to strike weakly. They way it will get stronger is through exercise, so I would give it harder prey. It isn't going to starve to death in a couple of weeks. Stomatopods are like my cat. It holds out for tuna, but after awhile it gives in and eats dried cat chow.
Roy