I actually had an interesting experience with the SAT the 2nd time I took it. I was on the second section (it was reading comp), and I had been doing quite well by my estimation. I breezed through the section with plenty of time to spare, and I spend almost the rest of the time twiddling my thumbs. With only about a minute to spare, I found, upon checking my work, that I had put the last 5 answers in the wrong section (section 1)! I frantically tried to put them in the right one, but time expired and I had only transferred 3 of the 5. And I was pretty sure I got the other 2 right, too. I never did erase the 5 answers to unasked questions, and I feared that this blunder would significantly alter my score in some way. I seriously considered canceling my scores. In hindsight, I'm quite lucky I didn't.