Of course, you should have read the question before writing the answer. However only reading it before you answer the question is very dangerous. It is surprisingly easy to find yourself answering what you thought the question was, only to find, on re-reading it, carefully, that it actually asked something else.
The temptation at this point is to pretty much make do with what you have written, and just change it a little. However you score no points for a good answer if it doesn’t answer the question! If it requires completely re-writing that is what you will need to do.
My tip is, read the question, re-read the question and read it again. In fact, keep on referring to the question until you are fully satisfied with the answer.