They want me to play Inside Line Backer.....Am i to small?

I'm on my school's jv football team, as a freshman. I'm 5'6 145 pounds i play running back on the other side of the ball. But my coach wants me to play strongside linebacker on defense i think i'm small. I can hit good and hard. I'll take ur teeth out u say the wrong thing to me in a game but i've seen the other school's lineman some are 6'4 300 pounds im 5'6 145 how am i supposed to break through those blocks and make the play