High school can be tough!
I don’t have it in me to write a long post, but here’s a few pieces of advice:
You aren’t the only new junior, try to connect with some of the others.
Find an activity that interests you (eg theater crew, managing a sports team, writing for the paper) you may find your tribe there.
Speak to a counselor.
Find other kids that could use a friend and befriend them.
Why did you decide to go to boarding school? Perhaps focus on those reasons.
Junior year is notoriously difficult, I expect the work will ramp up.
Finally this is the most difficult time. When you look back in a month’s time you will see how far you’ve come. It will get better!