Practice questions do not teach you. Practice questions test you. Mastering the material you need to raise your score is something that takes place in the studying you do before and after doing questions.
One of the laws of human behavior is that doing more of the same thing will likely net you the same result. You do not improve your chances of getting questions correct by simply doing more questions. Doing more does not change your behavior. Rather, you need to look at your thinking on each question and add to your knowledge base.
When you miss a practice question, first read the annotated answers. This should help you understand what the question writer intended, why the keyed answer is correct, and why the other options are wrong. Next, take a moment with the question. Think about how you would need to modify the stem of the question in order to make the other options correct. This will teach you what the essential information is in that particular question.
Wait, you are still not finished. Now open your study materials and review the area you missed. Not just the point you missed, but related content as well. If you did not know something, or were not able to apply the knowledge you had, this is your chance to close the gap. Missing a question creates what teachers like to call a "teachable moment." Knowing that you got a question wrong creates a motivation to learn what you need to get it right. When you study after missing a question, you are more likely to pay attention to the content, and much more likely to retain it.
The simple message here is that quantity is not a substitute for quality. Doing a lot of questions without using a process that helps you learn from the experience will not cause your score to improve. Your exam preparation begins by studying the important content to give you a base to work from. Once the base is in place, questions will help you pinpoint gaps in your knowledge and test your understanding by asking you about that content in unexpected ways. This experience should drive you to study more.
As you move back and forth between study and questions, and questions and study, you will notice that both your percentage of correct practice questions improves and that your comfort with the content increases at the same time.
Questions and study provide the vertical supports on the ladder you are climbing to a higher score. Balanced between these two resources, your effort cannot help but carry you where you want to go.