I had a student once who focused a great deal more on his grades than on his learning. English was not his favorite subject. School work was not his favorite pastime.
This student was excited beyond belief when he scored 98 on his 100 point paper. He was ecstatic! Unfortunately, he thought those points would let him coast a bit, so, he used class time to socialize and didn't focus on the work that he needed to get done. In fact he tried to bluff his way through one book.
He kept looking at his grade and not on the learning. Because of the choices he made, his grade slipped farther than he had anticipated.
Had he only focused on his learning and not overpay attention to his grade, he probably wouldn't have fallen quite so far as it did. He thought he had a B but coasted all the way to a C+. Mom wasn't happy. Dad wasn't happy. Student wasn't happy.
Focus not on the grade but on doing the best work that you can. If you make a minor mistake let it go...move on...learn from it...and make it up by doing the best you can in the work left to be done.