The preview only shows you how it will look basically (position) it will not show you the information you are writing in there nor will it show the item number, name or postage status. Just type your message and make sure it's correct. The rest you have to leave in the hands of ebay to fill once the sale happens.

The information you select will be what's on the message. If you can't see the scroll menu to select that then perhaps change browsers, I'm using firefox and it's showing fine.