Identify the poor word choice and replace it with a word of your own. the only puzzle with our plan was that it required me to stay out way after my curfew.

I would contend that the poor word choice is "puzzle" and it could be replaced with the words "problem," "obstacle," "setback" or "difficulty," among others.

Explanation: Just to elaborate a little on the answer, it can be added that the speaker is describing a plan, that is, an intention about what one is going to do. The plan might have already happened, but it is also possible to infer that, because of the way it was conceived, it did not come to fruition. For that reason I have used the words above (obstacle, setback, difficulty), because it seems that staying out way after his or her curfew was too much of a problem or a difficulty to effectively accomplish the plan. The word "puzzle" refers to something confusing or disconcerting, and, therefore, it is not suitable in this context.  

answer; membership group;