You seem to be overcomplicating this. Just remember the more general definition of free will: the ability to have acted differently.
To which I have pointed out that the progression of time does not allow two opposing decisions/actions to take place. You (the brain) cannot decide to sit, while simultaneously, to stand. It is one or the other in any instance in time.
So if you (the brain) make a costly error which you regret a moment after it had been made, it is obvious that had you been able to choose otherwise, you would have in order to avoid your regretted decision.
It is only with the progression of time and new information feed into the brain that enables you (the brain) to see the prior error, but then of course it's too late to change. We cannot go back in time and do things differently, no matter how strong our will or desire, nor can we do differently in any given moment in time, just what the information state of the brain in that instance in time allows.