edit the css to change the width for 100% to 976px.
in the WA_eCart/CSS/eC_Clean_boh_Arial.css
edit the width in the .eC_Clean_boh_Arial class:
.eC_Clean_boh_Arial {
color: #2c2d2e;
font-family: Arial,Helvetica,sans-serif;
font-size: x-small;
width: 976px;
}