You would need to have full admin access and likely the install-restore DVDs, plus
any other software in use in the computer, to correctly repair the computer now...
So that would be a matter involving the IT persons who oversee these school macs.
These ASC discussions are primarily unstaffed by Apple, and the persons who may
reply are mostly volunteers who are just product owners and users, like most others
who visit here. The situation where your school is concerned, involved a hierarchy of
permitted user access, an admin who should also be in charge of upgrades, repairs
and other maintenance duties; and lesser access accounts and limited permissions.
As one of the latter, you would have to find a pleasant way to suggest to the Admin
that you may have somehow messed up the system in that computer, and if you
knew more about how to fix it (maybe they can help you learn, hands on?) that it
would never happen again... cross fingers, etc. & hope not to dye, jokingly of course.
The system install discs, access, and the ability to restore all other user accounts
is part of the risk in messing around in a multiple system Admin managed system.
Good luck! 😐