[Plugin: JJ NextGen JQuery Slider] Center Image Not Working

So, I’ve got the plugin up and running here (https://merrellredway.com/). It works, however I am unable to the center=1 to work. I’ve pasted my shortcode as follows:
[jj-ngg-jquery-slider html_id="homepageslider" gallery="2" width="960" height="640" controlnav="false" center="1" order="sortorder" effect="fade"]

What am I doing wrong? I’ve set a width…

Thanks