Do you have a computer? Have them recreate the project on the
computer. Maybe make some changes to it (ie: monochromatic
color, etc). Have them recreate the project using alternate
materials (if no computer) or use the same subject in a
different way. Or the same media in a different way.
Basically, just extend the project. Last year my HS kids just
wanted to play cards when they finished. That was hard to
combat (I guess the previous teacher had let them), but finally
they "got it."