For orders that contain MTO (Made to Order) items such as tees, wallets, posters, mouse pads, etc., those MTO items only have a 24 hour window where they can be canceled. After that time, the item(s) cannot be canceled as the item(s) have been produced.
Aside from that, as long as your order does not have a tracking number assigned or has not been marked as “Shipped”, absolutely! If you have already been charged for your order in this case, you are able to receive a refund for the order as well. Please note that an order cannot be canceled if a tracking number has already been assigned to it. Note that canceled orders are not able to be reactivated or recovered.