It was alright for a short but not that original. This has been done before many times. Having said that, I liked your animation style and you did a decent job with setting up suspense in a short amount of time. However it was too predictable, we knew what was coming already, and maybe with something unexpected or diverting from the usual straightforward story.
As far as the music, I think this is one of those times where you were wrong and music would have elevated the scare factor tenfold. I think the silence just sort of gives it a very...amateurish sound. When the viewer keeps checking the sound to see if its "on" that takes them out of the movie. You don't want that. Just my opinion. Keep it up though.