Twenty Eleven – Width of posts

I’m having a problem squeezing some of my content into the standard post options in Twenty Eleven. (I do have a child theme installed for customizing.) I’m attempting to display some wide dynamic content. On pages I can display it correctly in the ‘Showcase’ template. I cannot get it to display in any of the post options. I’ve attempted to adjust the width of the content as follows:
Changed:

#content {
margin: 0 34% 0 7.6%;
width: 58.4%;
}

TO:

#content {
margin: 0 14% 0 7.6%;
width: 78.4%;
}

As an example, my page https://pghtix.com/tickets2/?evtid=1807418&event=Van+Halen displays correctly while similar post at https://pghtix.com/roger-waters-in-pittsburgh/ squashes the map image on the left side.