"Yes" should trigger whatever functionality we need to complete cancellation -- may differ depending on whether we've hit the back button from Amazon or the cancel-my-pledge link in pledge_modify.
Similarly. "Whoops" should use {{ try_again_url }} if we're coming out of Amazon, and should be a link back to the work page otherwise.
Not sure whether these want to be input buttons for forms, links, javascript, or what -- make them be whichever they need; I have applicable styling in any case. Will retrofit that.
This suggests we may need an if condition to determine which route we've come from since they may have different context (e.g. try_again_url I suspect only applies if we've come by way of the payment processor).