Thank you for providing the screenshots.
In Chrome 35 on iOS 6 (and in Mobile Safari, too), I see your web page as your 'before' image (not as you see it in Chrome on iOS 7). What version of Chrome are you running? If it is not the latest version, try updating it.
The only way I can make a web page 'zoom-out' in Chrome 35 on iOS 6 is to not use the following <meta> 'viewport' tag.
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
Try replacing this <meta> 'viewport' tag with the one which Juicebox now uses in the 'index.html' files generated by JuiceboxBuilder-Pro to see if this helps:
<meta name="viewport" id="jb-viewport" content="minimal-ui" />
Also, I notice that your gallery has a width of 100%. Try temporarily giving your gallery a fixed width (just for testing purposes) to see if this makes a difference (to see if the 100% width is somehow forcing the web page's width to expand resulting in a change to the scale of the web page).