No why should you cheat? I can actually tell you that I saw the papers for my science 2020 GCSE mocks since I was revising. It wasn't directly cheating but the thing is I did it so close to the test that I actually knew most of the answers. Even worse, those were the grades for my GCSE results last year, and I still feel guilty about 'cheating' to this day, since it wasn't a fair representation of myself. Honestly, even if you are stressed you can only give it your best shot and if you're usually a high achiever than its not going to affect you if you get one bad result.