Is my writing any good?

It's a good idea, but you don't go into enough detail, and the metal on bone sound thing was done twice. Also, some of the sentences are run-on. I'm 14 too, and have been writing for a while, so I know that this isn't all that bad. More detail though, and break it up more. Maybe something along the lines of "The sharp blade pierced the metal armor that was meant to protect her body, and sliced easily through Hayley Leto's strong form. The gasp she emitted was audible even to my ears, and I watched with horror as she coughed, spitting blood out onto Rafael's hand, staining her pale lips a dark red. As she slumped forward, feeble hands gripping the sword, he stepped backward, dragging the blade from her body with agonizing slowness. The grating sound of metal on bone sent chills up my spine and a sharp prickle across my scalp." Well, that wasn't all that great, but you get the picture. Horror is about gory detail. Lots of it.