How do you get to Hollow Bastion after sealing all the key holes in Kingdom Hearts 1?

I have sealed all the Keyholes so far and the next place i need to go is Hollow Bastion, It is Battle Level 50 and im only on Battle level 40 how do i get up to battle level 50 because i have been fighting enemies over and over again and its not earning me any points help please im stuck.