shrinkwrap will not work on an open or single surface model.
you will want to make this into a model that captures some volume. It does not need to be watertight, BUT it needs to be closed up well enough that shrinkwrap can fill the holes that remain. Also the holes cannot be larger than the setting on the edge length setting in Shrinkwrap.
a common fix for this is to make surfaces that overlap the holes, allowing the shapes to capture a closed volume see below-
