I have tried to get a template that would make the content area widen to cover the whole width of the screen without the blank sides.

I have tried editing the template.css that came with the siteground template,which ended up just messing it up all the more.

can someone help me out here?

Can you show us the site your trying to edit? You kinda asking us to fix a leaky pipe, but not telling us where the pipe is.

Is the template has fixed or fluid width, are the columns collapsible, can you assign width in back end?