You can do this, here's how. First you make the layout span the layout.
go to ATO->Style & configure LAYOUT->Layout Container Style and set the padding to '0px'. This will cause the entire layout to span the page width you defined. Next you add the indent(padding) to the left side. Since you are not using a left or left inner sidebar, you have to add the left padding to the 'middle', so go to ATO->Style & edit CENTER COLUMN->Center column style and change the 'padding' entry. You currently have: padding:50px
. This says 'add 50 px of padding to all sides of the area' but you only want it on tht left, top and bottom...well maybe some on the right to get it away from the sidebar. When you use the shorthand, the the four entries go 'top, right, bottom, left' so you want padding: 50px 10px 50px 50px;
or some variation like that depending on who big you want the spacing.
Lastly, there is an override in the CSS Inserts, so go to ATO->Add HTML/CSS Inserts->CSS Inserts and remve the entry
You could leave the right sidebar even with the edge, or add some padding (ATO->Style & configure SIDEBARS->RIGHT sidebar style)