Is there anyplace you could lock up the bike inside? In my school in downtown (high school) there is a designated hallway with hooks to hang up bikes, maybe there is something similar? If not, even if you could lock it to an indoor railing in view of a receptionist area or security camera would be safer than on the street.

I use a kryptonite mini-u to lock up my frame when I'm just inside for a few minutes and hope my lack of quick releases will deter casual thieves. I also have a kryptonite chain and padlock for longer term stays, and I haven't had anything stolen yet! (knock on wood)