While in the Gummi Ship menu, hit "X" to open up the garage. You can then click "Garage" to be given a list of the gummi ships you are able to edit. Use the "D" pad to cycle through blocks until you see one you have acquired by traveling between worlds or bough from shops, and attach it to your ship. After attaching something, hit "RB", the "B", and save your change. I simply added an additional wing, saved, and the achievement popped for me.