It is still possible to get a high atar, but you have to use these upcoming Christmas holidays to study hard and significantly improve your marks. Whatever you end up with in terms of rank and atar, this will all be determined by what you are willing to and going to do after this assessment. It is always possible to make up ranks and improve marks, but you need to identify what you did wrong in that assessment and how to improve from that and not do it again. This might be due to you not studying enough compared to the top people or you simply don't know what information is relevant to each specific question. If so for both of these possible reasons you could ask those top people if you can read their assessment, ask them for tips on what they did to prepare for the assessment and if they can look at your answers in the assessment to pin point where you have gone wrong, because there might be a trend across your answers of not doing something which if you could address could improve your marks. You need to identify that and then make your notes and do as many questions as you can and get them marked by your tutor or teacher.