Head First book itself is more than adequate for this exam. If you think that you should cover it again, do it. Also, try to go through exercises without any preparation and you'll get an idea about how much preparation is really needed.
Once you feel that you are ready for exam, then (and then only) attempt the test given at the end of book. But do not attempt it more than twice (the reason being, at third attempt, you'll clear the test because you'll remember all the answers ). If you can clear test given at the end of book, you can expect a good score at actual exam.