how to break up long list of radio buttons?

URL: http://www.fromwagstowishes.com/store/

This form integrates with cart66. There's only 1 product with 1 price, but there are 31 options for the product. Rather than a long scrolling page of 31 radio buttons, I thought I'd break up the options into 3 columns. Works beautifully visually, but the problem is that a viewer can click more than one radio button, which is problematic for adding a single product to the cart.

I think a dropdown is going to be cumbersome for the viewer, and I don't think check boxes will work for 'add to cart', so I'm stumped. Can you think of a workaround, or css solution to displaying a single set of radio buttons in 3 columns?

Thanks for taking a look -

HI David,
Thanks for the response.
I'm already using Ready Classes - that's how I got the 3 separate columns of radio buttons.

At issue though is how to break up 1 long list of radio buttons with ready classes... how can you apply ready classes to radio button options 11-20, and not the entire radio button field?

Duh! Didn't read far enough down the page.
Sorry to bother you - works perfectly!