At the point of doing the decision has been made. So yes when a decision has been made you act on that decision.
Perhaps I mislead you with "the point of doing." What I meant to convey was the point at which you seemingly "decided" to do X rather than Y, you could not have "decided" to do differently. Even the event of seemingly "deciding" to do something was predetermined by the cause/effect events leading up to that moment.
Prior to that decision that resultant action has not yet been determined.
But it was. Consider: if what you do was not caused then the only other way it could arise is utterly randomly, and I don't believe you want to claim that what you do is utterly ransom in nature. So, going back to the moment of "deciding"---where one would say one's will kicks into action---- there had to be something that caused you to do X rather than Y.
What was it? Propose whatever engine of conception you wish: mind, judgement, instinct, intellect, thinking, mentality, etc., there has to be some kind of operation that brings you to do X rather than Y. Exactly what caused your mind to arrive at the "decision" it did, and no other?
[Saying it's one's will is simply going back to the "deciding" point, which we've gotten past. (In effect, we're now looking at how the will works.)
] Going on, the mechanism of "deciding" has to rely on causation (randomness having been excluded), so the act of deciding was caused, but what created this cause? Well, again having dismissed randomness, this creating must have been caused, in turn making it's effect the cause of your "deciding." And this series of causes/effects goes on back to a whole lot of prior causes and effects. So your "deciding " to do X instead of Y was determined by all these prior causes and effects. A led to B, which lead to C, which lead to D, which lead to E, which to led your so called "decision." It was an inevitable out come, just like taking a particular set of roads to get from A to B. To get form A to K would necessitate taking another particular set of roads; however, because you took the first set of roads you had to arrive at B and not K. Your "decision" has to be what it is and nothing else..
A simplified illustration: