I've started loading products to get a better idea of layout and i'm not really happy with all the dead space, example below:

As you can see, there is a lot of empty space to the right of the cart etc, and below. I can shrink the dead space slightly by adding content to the right column, but what I would really like to do is lengthen the extra images section so that they run in a line underneath the review/share section.
I have tried editing the stylesheet to change the width....
.product-info .image-additional {
width: 260px;
...but while this works, it pushes the cart/review/share section right over to the right.
I'm new to all this so any suggestions would be greatly appreciated! I'll be using between 3 and 6 images per product.
Thank you x