Hey Yussif,
Yes, it is important to have an aim but when it gets to the point where thinking about the numbers makes your head spin, it might be helpful to just try your best and not focus too much on them.
In regards to ATARs, you are capable of getting any number that is possible with the system. There may be obstacles during VCE, but even if they do affect your performance, there is always a way into your preferred uni course.
Please don't let a number define your worth or your capabilities. Tests and exams are not you as a person. By the time you get to uni, the ATAR buzz will diminish and not many people will care about it anymore.
You're in Year 11 next year, so you have time to work out what kind of approach to schooling suits you and your strengths and weaknesses.
All the best
Edit: beaten by J_Rho