I need to make a simple instrument in 2 hours or less that has at least 5 pitches and change volume. Any ideas?

Maybe some sort of flute made from pvc pipe? With the short time frame, it really depends on what kind of tools and material you have lying about the house or at your disposal I guess...

Would some sort of percussion instrument work? At least that way the whole volume issue is controlled by how hard you hit it, no?

If that's the case, maybe a bottle xylophone would be the quickest thing to make.

All you need is five glass bottles, fill them with different amounts of water, place them in a stand, and use a drum stick or other similar item to play them.

If you're looking for something more intricate, then maybe the following video is what you should aim for (although good luck putting it together so quickly).