I figured I should try asking for help before I spend another hour trying to fix this on my own, just in case somebody had a quick answer.
Problem: Products extend beyond the edge of the page.
I have added padding (10px) and a margin (15px) to .centerColumn via the stylesheet to show the metallic border around product info. I also swapped the div class in tpl_index_product_list.php to ".centerSansColumn" to avoid having the cardboard background appear on the product list.
Anyone have any advice, other than setting up another temp store and seeing if a fresh install works? This was working earlier though, so I must have stroked something the wrong way... It just bugs me that I can't fix it without starting over (not completely reinstall, of course).
P.s. Forgive the header, logo, stolen products and other rough spots- I just threw those together to temporarily flesh things out.