Yes, that is correct. If your top face and bottom face laminates are unsymmetric (which yours are), then you must create a mirrored laminate (as you are proposing) for your bottom laminate.
If you were using symmetric laminates for the top and bottom facesheet, then you could just create the material one time and copy that material into both the top and bottom facesheet variables, or alternatively, you could use the "Link Top and Bottom Facesheet Materials" check box on the Concepts tab.
In your case, however, it would be best if you created separate laminates for the top and bottom face as you proposed.
