Can i make it show only once?

Hey support,
Thanks for great free plugin. I am using the popup on my checkout page, to try and sell my customers some socks. But when they click “Add to cart”, they are sent to the checkoutpage again with the socks added to their cart, and the socks popup will show again. I have chosen “Show only once per session”, but it still shows more times unfortunately ??
Is it possible to actually show it only once?
//Anders