I don't think there's a way to see trades rejected by you, only ones that other people rejected from you, but there's a way around this. You could look up the card in particular and see who wants it. You might then be able to recognize the user name of the person who you are trying to re-trade with on that Want list.
Another option is to go through your notifications (if you haven't deleted them all) and see if you see a "Transaction Proposal" notification from that user. Again, you'd have to recognize the user name, but if you aren't one to get flooded with offers from other people maybe the usernames to choose from will be short.