When the teacher lets you grade your own quiz, you’re not grading the quiz. You’re grading yourself.

The teacher has handed you a situation where the only thing actually being measured is you. Nobody is going to check, and the marks are not the valuable part anyway; what you learn is whether you can be trusted with something small. A point quietly awarded to yourself is a result about you, recorded in pencil.

Mark it strictly, especially the answer that was nearly right, and write the real number at the top. If you are not sure whether something counts, mark it wrong and ask afterwards. The score matters less than knowing your own figures are reliable.