Sorry for the delayed response. Was caught up with a update to the theme that I submitted today. For center aligning the menu, easiest option is to set a width to the primary menu, specially if you know the number of items that are going to sit there. Paste the following code into Custom CSS tab in theme options or anywhere else you prefer like in custom.css file in {theme directory}/custom/ folder –
#primary-menu > ul.menu { width: 730px; }