It shouldn't really hurt if the broken bones are being kept still.
There might be a background ache.
The sling is there to prevent your limb dangling and getting more swollen. If you can elevate your hand above your elbow any other way, do this; rest it on a pillow, put your hand in the air like a child in class, whatever.
Wiggle your fingers, while keeping your wrist above your elbow.
If you feel there something digging in or your cast feels tight, get someone who knows to take a LOOK.