When adding a card to your inventory, how about under the "Add Card" button it shows the Last Card you added.

Sometimes I'm entering cards and get interrupted and forget if I've entered a card or not. Maybe show the card name and then a button that says, "Add 1 More..." or something like that?

You have the possibility to order the entries in the inventory to "last added", so you can see what was the last card that you did add.