My Boyfriend threatended to kill me?

He just threatened to kill me maybe 10 minutes ago. He said "I swear to god, if you dont shut up, i'm going to slit your throat" So I said "B*stard!" And now i'm scared hes going to kill me. What should i do? I was gonna call 911 but i didnt. But we live down the sreet from eachother and go to the same school so how would i get a restraining order?