Lingua Latina is good for "left to right" reading -- that is, reading and understanding without translating word for word -- and for learning vocabulary in context.
It is not designed to teach students how to recite the principle parts of delere or to distinguish a objective genitive from a partitive genitive. And there's no guarantee that the material covered in a given chapter of Lingua Latina is the same as that which you need to know for the exam.
I would suggest that you take half an hour and look over your previous exams and figure out where you had the most difficulty (where you lost the most points). Was your problem with vocabulary? Identifying forms? Sorting out the various words in a sentence into some semblance of meaning?
Then go back over the grammar and reading material that will be covered on the exam and focus specifically on those areas which gave you particular difficulty.
FInally, you may already know this, but one key to getting good grades on exams is smart test-taking. Extrapolate from what you do know. For example, if you don't know the meaning of a verb in a sentence, don't give up and leave the entire sentence blank. Translate the parts you do understand. Use context to help you.
Are you taking a grammar course or a reading course?
In reading courses, I found that working through all the passages at least once helps enormously when reviewing. Not because I will remember every wierd construction or every vocabulary item, but because I remember the meaning of the text (or the process of deciphering it) and that seems to help me when I come to the exam.
IPHIGENIE: Kann uns zum Vaterland die Fremde werden?
ARKAS: Und dir ist fremd das Vaterland geworden.
IPHIGENIE: Das ist's, warum mein blutend Herz nicht heilt.
(Goethe, Iphigenie auf Tauris)