I need a Little Help with a project

Firstly, I'd advise you to really clean up the code on the page.
Use CSS rather than line-breaks and random blank paragraphs to space out your content.

Now on to the issue itself.

The <div class="content"> in which the digital book is nested - you should rename that to something else... Something more relevant. Since the feature is unique (to this page anyway), you could use id instead of class. It really depends what you have planned for the website.

Anyway, once that's done, add this little piece of CSS to any of your stylesheets:

div .digitalbook table {margin: 10px auto; text-align: center; clear: both;}

In this example, I assumed that the class name of the div is digitalbook. If you opt for the id version, then use #digitalbook instead of .digitalbook

Should work, if all tags are correctly matched..