A perfect 1600 score on the SAT Exam does not necessarily mean you need to be 100% perfect in all the questions. Luckily, there is some breathing room for certain sections that allow for a few mistakes if you answer a question incorrectly.
In the Math section, you must answer ALL questions correctly. Generally speaking, if you miss just even ONE question on the Math section of the SAT Exam, the score will NOT be 800 in that section.
In the Reading and Writing section, you can miss 1 or 2 questions and still receive a perfect 800 score in that section.
Perfection is hard to attain and sometimes it is hard to predict how the College Board will evaluate your score. It is best to aim for an absolute top score with no wrong answers on questions for the best chance of getting a perfect score of 1600 as a final composite score on the SAT Exam.