Fortunately you've got some weeks to do some solid learning.
20 new words/phrases a day ( half an hour), say them out loud, cover first the English and look at the German, then vice versa until you know the spelling, gender- and a phrase you could use them in.....go over yesterday's with the new ones. So by the end of the week you will have covered 140 . Language learning is all about repetition. Verbs are a killer for lots of people. Do you know them? All the irregular ones?
Learn the vocab, phrases, verbs in groups according to the topics.
Look at the language requirements for the essay question. Are they going to mark you on eg compound verbs, idiomatic phrases, ...
make a list of sentences using them so ... Once I had studied../ seen (pluperfect): if I had thought about... I would have realised....(conditional perfect....) etc.
Make a list of the sort of phrases you could use in any essay - so, first of all, on the one hand... on the other, in my opinion, after having considered all possibilities, in the end, whatever we think about...., and make sure you can use then accurately. Half your essay will have been done before you even get in the exam room.
I know it sounds strange but you should know more or less what you are going to write before you go into the exam. You should have prepared an outline of paragraphs using link words, the idioms you want to get in, the complicated verbs you want to use. All you have to do is choose the topic and slot the tenses, phrases etc, into it.
As soon as you are told to start write down the idiomatic phases you want to use, to make sure you do.
Many people think you can't revise, prepare for a language exam. They fail.