Here it goes.
Things to note while editing css.
To get the centre piece to align on the right of the first sidebar, never use margins, use float: left.
You have used margin for the sidebar on the right too. margin-left :736px; Do this with floats.
HERE IS the SOLUTION
The class container contains both sidebars and the center. Always make sure “content” class’s width is equal to the width of sidebar1+sidebar2+center+margins+paddings. Make the pixel count correct and your theme will be fixed.