WooCommerce One Page Checkout Plugin doesn't work on mobile

I have WooCommerce one page checkout plugin installed on trafficschoolnv.com

and the checkout page doesn't show properly in mobile display.
This is what it looks like on a mobile browser (both android & iOS) I'm not too sure if I have to alter the PHP to have it display in a mobile browser different. What would you recommend?

via Chebli Mohamed