You may think what is the easy way to add a column that has the same width the header, and is located right above the main and sidebar, without the need to add html code.
Blogspot actually has provided code that can be activated for these purposes. When you are in the "edit html", try to find the code below and change the status showaddelement from "no" to "yes" and then save.
<div id='crosscol-wrapper' style='text-align:center'>
<b:section class='crosscol' id='crosscol' showaddelement='no'/></div>
<b:section class='crosscol' id='crosscol' showaddelement='no'/></div>
