To make it less afraid? start by just spending time with it, not holding it but just quietly sitting beside it's brooder talking quietly, don't place it's brooder in the most heavily moving areas of your home, ducks startle easily. coming in from the top can cause panic since they are prey...
I think that maybe a Muscovy duckling, Do you have Muscovy's living near by? they don't migrate. unless you live in Texas... Does the lil one have a stuffed animal to cuddle with and also a non breakable mirror will help it feel secure.Does it have a pointed tip to it's bill?
here is some...
Call the rehab center they maybe willing to meet you half way. sometimes they have people traveling that will take animals to a different location. So you never know till you try. If you have harsh winters and your wild duck is one that migrates you may end up having to keep it inside to keep it...