penny whistle

This may be sort of a "duh" question, but I have to ask. My church has been playing "Be Thou my Vision" for quite a while, and I thought a whistle would sound so good there. I went to my local music store and bought a $12.95 metal whistle with a plastic mouthpiece. I can play the song, but it sounds sort of like a new violin player trying to learn how to use a bow. Esp the upper register
My question---is that because I need more practice to cover the holes better (I do play indian flute). Or is it likely that it is because it is not the quality of whistle needed to play serious music.