Ok, so I decided to put a player on the transfer list, and for some reason I bid on him. Is there any way to undo this?
No, unfortunately there is no mechanism to retract bids, whether you placed them on your own or any other team's player. Bidding on your own player of course is also not against the rules (though some people feel compelled to report such cases), but obviously if you were wanting to sell him and instead bid on him and maybe end up winning that would be less than ideal.