some anxiety tips?

ive been doing online school since last march when the pandemic started, and recently any thoughts about going into that building again make me nauseated and my worrying goes through the roof. I have my PSAT tmr morning and im trying to go to bed but the anxiety of thinking abt how im going into school tomorrow is keeping me up, i really dont wanna over exaggerate but i genuinely dont know how to calm down. im not worried about my grade because im sure ill do fine i just genuinely cant explain it.