I will be appearing for the SAT with essay next month. However I am confused about one thing- are we allowed to use abbreviations like "we're" (we are) and "it's" (it is) in the essay section? Will it be considered against me? As an Indian, we were told not to write such abbreviations in our ICSE 10th board examinations.
At one time, contractions were strictly forbidden in formal writing, and essays were considered formal writing. In more recent times, neither is a strict rule, since a more informal style has become more common across the board.
However, it's probably safer to go with the stricter interpretation, since you don't know who will be grading your essay.
With that said, it might depend on the writing prompt. If the topic is something personal, a more informal style may be more appropriate. If it's on a scientific topic, or a moral or philosophical topic, I'd err on the side of formality. (One warning: my own SAT days are 25 years in the past!)
This website shows the rubric used to grade SAT tests. It does not discuss contractions anywhere. So I believe that as long as you use a style that fits the criteria described by the rubric, whether to use contractions is a stylistic choice you can make for yourself.