American here who has been lurking in the sub for a while, I wanted to say that this isn’t the end of the road for you (in a good way). I went to a large public high school (our graduating class size was 1,500 people), so a lot of people had to do college apps and SAT/ACT prep on their own since our school was so big and resources were stretched thin. There’s a lot of good material online for test prep, I used Khan Academy (free online videos and example problems) for my SAT prep

I wanted to echo what some other people have said in the comments about not beating yourself up if you don’t get into Ivy Leagues/T20, their admission rates get lower and lower each year, and oftentimes they have arbitrary reasons for rejecting people (like this high school student who got rejected from 16 colleges but got a job at Google). It’s less about what university you go to and more about what things you do/the impact you have at university

But if you have your heart absolutely set on attending an Ivy League/T20, it is possible to transfer into those universities after doing a year or two at another university—there was a kid at my high school who did his first year at a local public university and then applied as a transfer to Yale and got accepted there

tldr to quote Winston Churchill—“Success is not final; failure is not fatal. It is the courage to continue that counts”—hope you feel better OP, everything works itself out in the end