I wanted to let you know that I've implemented the option to keep the scimitar instead of giving it back to the shopkeeper. It's included in the next update.
Sorry for the confusion. The Scimitar card is not in the current version. Right now you only have the option to get some money from Cedric (the shopkeeper) by finishing the quest. However, the scimitar card will be added in the upcoming version, where it will be available in the shop if you give the weapon back to Cedric, or (if you keep the card) it will be added to your inventory and Cedric will be very angry.