Swiggy — I have been charged 100% cancellation fee

I ordered an item through their app but of some reason i mistakely ordered another item so then i want to cancel it, but the order wasn't prepared and the customer care kept asking me they will 100%cancellation fee which i didn't understand at that time.
I will not ask my refund if the order was prepared or out for delivery because it will be the loss of restaurant but in my condition that's not the case