Hi Dawn, welcome to the site. These big BOP's should be getting larger and larger leaves. In my garden here, they are in the ground, and get to be 20ft. tall even competing with the roots of oak trees. The largest leaves can be 8ft. long not including the stems.
I'm sure you need to pot that plant up into a much bigger pot, and fertilize it some at the beginning of its growing season each year - that would be just when you're ready to put it outdoors for the summer. Don't be afraid to water it, they can take any amount of water as long as the drainage is good.
That being said, white BOP's really aren't good container plants unless you have a 2 story conservatory, or a shopping mall. They get huge.