How to Stop Making Stupid Mistakes
I had a student come to me trying to get back "lost points" on an exam, because the lost points dropped hm below what was needed to get an A, and he got an A- instead. This was in spite of the fact that his answers were demonstrably wrong.

When I spoke with him, he said that he needed to have the top grades in the class, because he didn't know how else he could demonstrate that he was a "good student." I had to explain to him that the degree to which he was insisting on a regrade (effectively demanding that he be awarded the points, even though they hadn't been earned) actually could hurt him in the long run, because it turns people "off"—no one wants to work with an inveterate complainer. And, ultimately, if he wanted to go further in either the academic world or in a professional career, what he needs are good letters of recommendation from people who are willing to vouch for him and support his career.

My reason for including such a long-winded anecdote here is that the underlying issues are the same: don't worry about little issues here and there. (That doesn't mean don't complain if there's a big problem—clerical errors and mistakes do happen!) Small mistakes are a part of life, and we learn more from those mistakes than from successes.

Nobody is going to think poorly of you because you make small mistakes. Just keep doing what you're doing, and try not to stress out about it when taking exams and doing your work. Worrying about perfection is a good way not to achieve it.