in the CSSFormBuilder/FD_Standout_Default.css, increase the width of the form.Standout_Default element.
form.Standout_Default {
background-color:#999999;
padding:60px 60px 60px 60px;
font-size:11pt;
font-family:Futura, "Trebuchet MS", Helvetica, sans-serif;
width:20em;
}