How important is it to write a perfect essay?
Usually, I persuade students I tutor not to be perfectionists and target at a quality essay rather than a perfect one. Targeting at “perfect” makes you waste a lot of time, it makes you afraid of mistakes and confused. Instead, when you aim at writing a quality essay corresponding to all demands, you may eventually finish with a perfect essay impressing your teacher.
One exception is an application essay. Here, I do recommend to seek perfection, because your task is to impress, to be remembered. Do everything you can and be sure to have your essay edited and proofread properly for you need to make the most of the chance you have.