Playing around with this duplicate of your template under <Template> and <html> I opened the hidden lines under line 7 and found that it is "Minima Black" dated 26 Feb 2004 - congratulations, Barb, your Blog template is old enough to go to High School! ('v')
Using the instructions on Choozurmobile "Modify Blog Widths, For Old and New Blogger Templates" <http://www.choozurmobile.com/2013/09/modify-blog-widths-for-old-and-new.html>
Given that "Main Wrapper + Side Wrapper + Margin = Outer Wrapper"
Which (from line 142 onwards) is "410 + 220 + xxxx = 660
and that I didn't want to change side wrapper or margin, I intially tried increasing the main wrapper and the Outer wrapper by 100px each - ie adding about 1/4 to the main wrapper.
and it worked!