Hi Jon,
Try centering the gallery's containing div inside the 'content' div by adding 'margin:auto' (for width) to the 'pg-gl' class in common.css at about line 11:
.pg-gl {
background-color:#1E1E1E;
font-family:Arial,Helvetica,sans-serif;
margin:16px auto 0; /* Add this line */
padding:8px 0 8px 8px;
width:720px;
}