Hi,
What you list on ebay from Auctiva is placed in your Store and added to the Scrolling Gallery (SG) automatically, not vice versa. There's a little more finess to the rules of what's currently showing in the SG, as there is a limit of 16 (I think that's the current maximum).
There is a sort of Preview of your Store look when you customize Store, i.e. it's template, header, etc., which you can view from the "Your default Store Domain Name:" link on the Store tab page. My store is empty right now, but you can see my very simple customization as an example, using the link in my signature.
Danno