Whatever you do, do NOT experiment with new words/ grammar in the real exam. The place to experiment is in the classroom, in your homework and practice tests. In the real exam. however, do NOT use the more complex language if you are not completely sure of how/ where to use it or how to spell/ pronounce it. Use the language you are confident and comfortable with. It is better to be simple and correct than complex and wrong.
Vocabulary:
to be under the impression = to believe/ think that
complex (adj) = complicated
accurate (adj) = correct