One other person has mentioned that problem. Not sure why that is, as I have the HTML for the text set at 600 pixels, which should span about as wide as the text on an 8 x 11 sheet of paper. At the time I asked a few folks to check some posts, and all saw them as I posted them.
I've got five different browsers on my Mac and my posts show up at 600 wide on each of them. Maybe there's something going on with your browser settings? I dunno.