pages to epub: missing text

I followed all the styles given from apple (http://support.apple.com/kb/HT4168)

I am done formating my book and ready to publish it.

When I export to epub, and open it on the ipad:

-some of the pages (that are suposed to have text) are blank,

-some are only showing some paragraphs and not others,

-some are missing the headlines, chapter numbers... very ramdomly.

I am not sure what to do! please help!

thanks