Mine came with a battlecruiser hull. Having compared the saucer with all the other hulls in the fleet box, it didn't match up with any of them, so I think it's meant to have its own hull type instead.
The best bet is to get in touch with Mongoose regarding it - they're a good bunch and will no doubt get you the correct hull sorted out. Besides, they can't do anything to stop such hiccups in the system if they aren't told about them in the first place.