Did you skip past enemy encounters or anything like that? I just find it hard to believe that you are so lowly leveled. I'm at Symphony of Sorcery at the moment and my Riku and Sora are at 29 and 33 respectively.
I don't feel like I skipped out on too many battles. ;x
I did skip battles almost all the battles in SoS, I rushed through that world, in an attempt to finish the game before my sister.