Can somebody please help me with a ps 2 game?

I am playing Kingdom hearts and I am stuck. I am at I think level 12. I am ay Hollow Bastion and I keep going from there to Merlin's house to the marletplace<<<<< HOW do I get on the next planet? How do I get the gummy ship back? Someome please help me as I am about to loose my mind here. I have been stuck on this since yesterday Thanks