I go to a very rigorous high School, that is one of the best private high schools in the state that I live in. I am in many
honors classes and have a 4.0 grade point average. Since my high school is so competitive many people apply to AP classes with over a 4.0, and even though I am qualified to take the classes, I am not getting in. I am still a sophomore but nervous because I am hoping to get into competitive collages, any advice? Thank you.
Six to eight should be more than enough. Really, anything over six is overkill. Focus on rigorous AP courses and do well in them rather than on numbers of courses. If you’re going to STEM, think about Calc BC, Chemistry, Physics, etc. Then, if you want more, think about the easier AP courses like stats, languages, bio. The colleges will already know the rigor of your high school, so you don’t have to worry quite so much about taking AP. There will be kids who will take more AP courses and maybe some self-study and the test, but have some strong ECs instead. ECs will grab the interest of the most elite colleges more than numbers of APs, and without strong ECs you’re not going to the most elite schools.
Six to eight over 4 years, not all in one year 
I totally agree with the above.