I believe the CSS for the Post Pins comes from dynamic settings based on the width of columns, and width of the gutter, as opposed to CSS settings you'll find in Firebug. Try changing the settings to 4 columns and I suspect the 1100px will fill out.
As you can see from the CSS you showed above, the height in that code is fixed, but Post Pins height is not fixed, but dynamic. To an extent, the width is the same, based solely on settings. The element.style CSS element represents CSS generated by settings.
If you go to the page where the pins are located, scroll down to PageLines Meta Settings and change the width of the pins to either a narrower or wider value, you will adjust the total width of the columns. Right now, it's creating 280px wide columns, plus adding 10px padding, plus margins, so that's setting the number of columns and total width.
Let us know what happens if you modify the width to 260 or 320.