I think mock exams are meant to be the roughest of guides in terms of content, and of course, they are a fraction of the size.
The biggest difference, though, is that in a mock exam, you control the environment 100%. When you take the official test, you have no (direct) control over: your health that day, your nerves (excited, nervous, scared, etc), sleepiness, quietness/loudness of other people, quality of the audio being played, time of day, lighting, etc.
We (as people) want to say that those little things aren't enough to sway us, but they are HUGE factors in how people deal with tests and other high-stress situations. Given the right variables, and it'll actually be harder to recall the material you do know!
All of these are hard to simulate with a mock exam.
Additionally, keep in mind that there is no such thing as "n2 kanji" - this is a misconception.
Many years ago (back when I was younger and took the jlpt), there WERE published lists of kanji, vocabulary, and grammar for each of the levels. Even in those tests, though, they would say "(something like) 10-20% of the content will not be part of these lists"
When they revised the JLPT exam in 2010, they officially unpublished all of those lists. That means that every list of JLPT materials out there (including renshuu) are best-guess estimations of what might appear on those tests. Because of that, we've been revising our lists to go a bit overboard in the number of terms for n5 and n4, for example - we'd rather you be overprepared than underprepared. It's a long process to get all of that done.
Not passing can be frustrating, but it happens to ALL of us. You can do it next time!
