Try deleting the book from the bookshelf in the iBoooks app and redownload it via the Purchased tab in the ibookstore in the iBooks app (the book's description page in the store says that it is the full 500 page book).
If it re-downloads in the same state then try the 'report a problem' link from your purchase history : log into your account on your computer's iTunes via Store > View My Account (Store > View My Apple ID on iTunes 11) and you should then see a Purchase History section with a 'see all' link to the right of it ; click on that and you should see a list of your purchases ; find that ibook and use the 'Report a Problem' link and fill in details about the problem (iTunes support should reply within, I think, about 24 hours).
Some people have had a problem with the 'report a problem' link (it's been taking people to this site on a browser instead of showing a form in iTunes) - if it does that to you then try contacting iTunes support via this page : http://www.apple.com/support/itunes/contact/- click on Contact iTunes Store Support on the right-hand side of the page.