If you are referring to the desktop layout, (line 641 in layout.css) change the width to suit.
Personal note, aesthetically, I prefer the width of your Photo page over the width of your other pages.
/* Desktop Layout: 769px to a max of 1232px. Inherits styles from: Mobile Layout and Tablet Layout. */
@media only screen and (min-width: 769px) {
.gridContainer {
width: 88.2%;
max-width: 1232px;
padding-left: 0.9%;
padding-right: 0.9%;
margin: auto;
}