I get that you want to encourage people and things, but maybe not say that the piece of paper doesn't define you...
1) That's a bit cliché, no offence.
2) That's what the vast majority of employers and further educators look at.
What you can say is that it's not the end of the world. If you get D's or U's or whatever, even if you get a B and that is hell for you, it is not the end. A Levels are much more important, and every single problem has a solution.
So when it comes to seeing your results, if you're not happy then talk to your teachers and research what you can do, just don't wallow about it as if it's the end of the world and nothing can be done. Some of the greatest minds in the world failed at convectional education, as well as some of them exceeding. You could be either or.
Good Luck everyone!