The position of that div is fixed to 50%. However, that's conflicting with your template or other divs on the page. I adjusted it to 70% and it looks more centered to me:
From /joomla/media/sourcecoast/css/common.css around line 33, I changed it from 50 to 70. This should help.
.sourcecoast.modal {
left:70%;
}
-Melissa