Complex sentence: Jamal must either admit Forrester's influence on his work or prove he had Forrester's permission to use his material, and refuses to do either, exempting his entry from the competition and endangering his standing at the school.
Split into simpler sentences: Jamal must either admit Forrester's influence on his work or prove he had Forrester's permission to use his material. He refuses to do either, exempting his entry from the competition and endangering his standing at the school.