A: Well, a lot of this depends on how the rest of the gaming group feels about this. I think we would be pretty lenient, especially if you realized it relatively quickly, so that it didn’t affect the game that much. We’d certainly allow you to draw up to the correct amount. It’s that little “take-back” that’s going to be controversial.
For example, if what you’ve played significantly impacts the game and the other players (like maybe making everyone discard a bunch of cards or something) then you realized that you wanted to take that play back, we might rule that while you DO get to draw up to what you should have drawn, you need to stick with that first play, and not change it. In the vast majority of cases, however, we’d be inclined to let someone have a rapid single-card “undo”, assuming your request was fast and the undo was relatively easy.
Again, it’s going to depend a lot on how the other players feel about it — and you should check with them as soon as you realize your error, and ASK if it’s okay with everyone that you take your play back, draw correctly to realize your full options, and then choose your play. You don’t want anybody getting bent out of shape AFTER they see that your revised card choice affects them negatively, when your first didn’t.