You might try clearing your cache after making changes.
Did you set the width of the divs in CSS? Take a look here for a template I dont use anymore that is centered : http://www.oolio.com/
In order to center a template, add this to the div you want to center:
margin-left:auto;
margin-right:auto;
If you want to add some space on either side of the blog, then you should add padding to the body element. Good luck working it out!
