It looks like the white line you refer to is visible in desktop browsers, too.
There is a horizontal scroll bar on your web page and if you scroll to the right, you should see the white line.
It seems to be spanning the whole content of your page rather than just your gallery so I don't think the gallery is the root of the problem.
I'm pretty sure it wasn't there until I did the recent 1.4.4 update
You could test this theory by reverting to whatever version you used before the update. I don't think it will help but it might eliminate (or point towards) Juicebox v1.4.4 being a possible cause.
Also, you could temporarily replace the gallery with just a plain empty <div> with the same dimensions that your gallery would have to see if the gallery has any effect or not.
Being that the white line is visible in desktop browsers, it might be a little easier to troubleshoot using your browser's developer tools.
I notice that if you prevent the 'bootstrap.min.css' file from being loaded, the horizontal scrollbar goes away and the thick white line to the right of the content is spit evenly into two thin white lines to the left and right of the content.
I think the layout of your page is somehow the root of your problem but, unfortunately, there is a large amount of CSS on your page (in several external files) and pinpointing the exact cause of the problem might be difficult (although I'd start be searching through your CSS looking for margin and padding rules).
I hope this at least points you in the right direction.
With regard to the meta viewport tag, the version of the tag in our blog entry is required only for full-browser gallery pages (where the gallery has dimensions of 100% x 100% and is the only content on the page). As your gallery is embedded in your web page alongside other content, this tag is not required and you can just keep your existing tag.
As the long tag contains all the 'content' that your existing tag uses, you could just replace your existing tag with the long version (if you were to use it).