Hi! I go to a top 10 selective school and have friends from Sbhs too so thought i could help. We students thrive off the competition. It's what drives you to do better, be better. As for average, its quite literally just an average. There is absolutely no point in comparing yourself to the average mark unless you strive to be average, however, you sound very young so i wouldn't be concerned about that too much. That said you can expect the averages and marks of students at these selective schools to be a lot higher and the environment alot more competitive and maybe a little more stressful than your previous school, but the truth is give it around 2 months and you'll get used to it. Good luck for next year!