They aren't centered because default styling on the UL is to add left padding.
Add padding: 0;
and problem solved. If you don't want the horizontal lines to stretch the full width you could balance out the padding (E.g. padding: 0 1em;
).
.pricing-table .plan ul {
list-style: none;
padding: 0;
margin: 0;
-moz-border-radius: 0 0 5px 5px;
-webkit-border-radius: 0 0 5px 5px;
border-radius: 0 0 5px 5px;
}