Don't worry, you've not tried to cheat in any way, and considering you were closely supervised, they would know that the second time you did it, you knew you would be watched anyway, so they're would be no point in forgetting to tick the box on purpose, I don't think they are suspicious, I think she was just annoyed as she probably wanted to get the papers sealed up and sent away but having the wait for you to find your paper and tick the box is delaying them, but that's not your fault, you have every right to be stressed out and its easy to forget things.