Step 4: Apply fixative (clear finish)
Krylon says that their sprays are safe to use indoors, and it won't affect your work surface. But you can always spray it outdoors, or at least lay your piece on some scrap paper before spraying, if you're concerned about it.
Be sure to completely cover your piece with the fixative. It may buckle the paper a bit when first applied, but once dried the paper will lie flat again. It should only take about 5 minutes or less to dry, but make sure that it is completely dry before moving on to the next step.