You can see your deck and the cards by going to the "Girls" tab. The one where you unlocked them. The bar on the right side has a card icon at the bottom now. You can see and edit any girl's deck there. If you only have 2 cards, there isn't a lot to do. If you have several, you can sort of pick the order, but the girl's special will get thrown in there randomly, too.
The game gave you the option to choose a girl? That is good. I didn't get that, but I drew pretty soon after it came out.
The cards seem to persist. I haven't noticed cards weakening, and I have been trying to get a feel for which ones I like using. That means using the same ones repeatedly.