All marks have some effect on your ATAR, whether big or small. What's happened has happened - you are best now to identify how to improve, work on that, and increase your marks for your next assessment/exam.
Remember your marks determine your ranks, not the other way around. You need to get good marks in order to rank higher. You don't go into a test thinking I need to come 5th. You go in thinking I should try to get 100%. You aim for marks.