for every form element that you add to the checkout page, you will need to add 2 things to the confirm page:
1) the confimr page has a collection of hidden form elements to capture the values posted from the checkout page, you need to add a new hidden form element with the same name as the one from the checkout page
2) Each form element has a corespondin set session value behavior on the confirm page.
on the sever behaviors panel, click the plus button and select eCart -> General -> Set Session Value.
see this thread for details: