The point of a GCSE exam in English Lit is writing a cogent and coherent analytical text – if you try to impress the examiner by using overly complex vocabulary you will disturb the flow of your analysis. This strategy will most likely make you lose marks.
Besides, it's literature, not language. The main skills you're supposed to show are the ability to structure an essay, communicate efficiently, a creative literary appreciation and knowledge of the texts you studied. By all means use relevant literary vocabulary when appropriate, but simple concepts such as 'narrative' or 'character', while sounding absolutely unimpressive, are still congruent with literary appreciation and will give you marks.