Music for my Film

I have begun to put music on my short film. My choice is a piece of music on GarageBand called Ambient Noise Effect 12, which sounds eerie and spooky, and would make the audience feel on the edge of their seat. Although I need a piece of music which is roughly six to seven seconds long, and the piece of music on GarageBand is sixteen seconds long, and if I was to cut it, it wouldn't sound the same and have the same scariness effect on the audience. An alternative thing to do is to create a short piece of music on a keyboard, which can be connected to GarageBand. This would be easier because I know how long the piece of music would have to be.