Sarah,
Here are two options for you:
1. As for the fingerprints, let the resin continue to cure. Recoat it with another layer of resin. As long as the resin isnt cloudy or smudged looking, it should be fine.
2. As for sanding resin, start with a coarse grit (400 to 600 or so), then work your way down to a very fine grit (1000 to 2000 grit — you can get the super fine stuff at a art parts store). Once you have finished it with the fine grit sandpaper, coat it again. It should be fine.