It’s a matter of days away now so I’d be sorely tempted to sit on my hands and wait.
At the risk of being totally wrong, I’d like to think next quarter will have a few more cars added and APs reducing a little across the board. Of course, AP reductions tend to be greatest on cars the manufacturer isn’t shifting via normal sales channels and/or models coming close to refresh or withdrawal.
You are completely able to cancel to the point at which you enter your PIN when you collect your car. Living where I do, there’s not a lot of choice of local dealers so I’d be tempted not to cancel for the sake of it for fear of having my card marked, so to speak.