"My score should have been higher -- I just made careless errors"

This is the single most common mistake students make. Careless errors are not random bad luck you can subtract from your score. They're systematic, predictable patterns in how you work, and they are your actual performance. If you got a 153 and made 5 careless errors, your score isn't "really" a 158. Your score is 153, and it stays 153 until you fix the process that produces those errors.