Hmmm... I had experience with the ACET (Ateneo Exam if I am not mistaken) and generally the essay should be a lot longer than that.
A few mistakes I noticed
knowing oneself is the entity's foundation
I dont think entity is a good word choice, try "foundation of personal growth" or something.
As an essay, its not very coherent. There is no clear narrative and transition between paragrahps. An expansion of the discussion on pressures experienced during your school days along with how it transformed you as an individual is necessary. Provide more details rather than the abstract diamond example.
But if you try to widen your perspective on such thing, you'll realize it is But for me, I take it as a challenge. Besides, just like diamond, its basic form of it is carbon, but through pressure, it became diamond, and let itself shine.
I dont really understand this part, Widen your perspective on what? Realize what? Its not very informative.
A better rephrase of the last line will be, "Carbon, through pressure, becomes diamond. And it is the diamond that lights the world." or something like that :D
Good Luck! ^_^