All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
You are not allowed to remove your Hijab for the reason you mentioned. You have to convince the school management that religiously you can not uncover yourself. If they do not approve then you have to move to another school where your religion is respected or continue the study from home. See Fataawa 90143 and 83135.
Allaah Knows best.