Try to distinguish between things that are in your control (who you choose as your friends) and those things that are out of your control (how other kids in your school act). Spend your time working on those things that are in your control and find a way to let go of the other stuff.
When your worries are taking over your day it could be helpful to set aside some time to worry on purpose: https://app.beme.com/co/1yoUBUtz5/time-to-worry-on-purpose
