I missed the exam for twice, and passed it on the third time. The exam was the same as others. After the exam I was interviewed by a judge, a very nice lady. She just asked me the reasons for missing the exam, and what was I doing for living.
This happened when I lived in Montreal, but I think here should be similar. So prepare to answer ( reasonable) why 错过了两次入籍考试, and take it easy.
By the way, show up earlier. I missed second time just because I arrived 20 minutes later than scheduled time. You know, the traffic in Montreal in the snow day. Here maybe better.