Place the star, curved side down, on a steel block. Tap it with a rawhide hammer until it is flat. File the edges of the star with a metal hand file until they are smooth. An acrylic nail file is helpful for a final sanding.
Pro Tip: Tool Tip: When using a hand file, remember to file in the opposite direction from which the teeth run. That is, make contact with the metal as the file moves away from you, using a pushing motion.