I agree with bulesz.
In fact I think that css templating in general is a pain in the a***
You can download and try several sobi2 templates, available in the sobi2 forum or the sigsiu download page, and see if you got one that visually approaches what you want to achieve.
Then you can fine tune it with css.
You'll probably have to modify any of these files (or maybe all three):
com_sobi2.css -- sobi2 component's css
your-sobi-2-template.css -- the css of your selected sobi2 template
your-joomla-template.css -- your joomla template css, very unlikely, but who knows...
And if you use any other sobi2 related module or plugin, probably their css file too.
I made this before but not being a coder
for me It's a hard work but firefox + firebug extension are my best friends there
So, to solve the adjusting to display problem I would examine the page with firebug and see where in the css files is the 100% width problem. I suppose that there must be some <div> that has a class defined with "width: 100%" somewere. With Firebug you'll find it easily.
I find very valuable the bulesz instructions about classes, thanks!
Good luck