When I view your gallery in Chrome (and Firefox), your gallery is not truncated, although it is necessary to scroll down to see the bottom of the gallery.
If you want to display your web page's header and have the gallery take up the remainder of the page (without the need for any scroll bars), then please see the View Resizable Gallery with Top Menu Example in the Embedding Multiple Galleries support section.
You can view the source of the sample web page in your browser and adapt it to suit your own needs (replacing the content of the 'header' <div> with your own header and swapping the sample gallery for your own).

You also have some CSS on your web page which is currently conflicting with the gallery.
However, this seems to be due to HTML errors on your page. (There is an <img> tag without a closing > on line 65 which seems to be resulting in your Juicebox gallery being included in your 'logo' <div> and inheriting some CSS rules intended for only the 'logo' <div>.)
You can check the code on your web page with the W3C Markup Validation Service and fix the errors reported.
This should hopefully fix the layout issues.