sounds like you're doing it right. Some hedgehogs will just ball and hiss and pop for a while and others will come right out and squirm around.
When I turn Quigly on his back he's usually open enough that I can see his nose but nothing else. If gently stroke up his nose from the tip to the quills he opens slowly and eventually squirms to get down.
Some hedgehogs are ok being on their backs, others hate it and will squirm and wiggle. Widget does the hedgie scream of death if I hold him on his back for more than 10 seconds. He wiggles and when that doesn't work, he screams just so I know he'es serious. :lol:
Widget is on my hedgie family page. http://www.freewebs.com/thehedgieden/ourhedgiefamily.htm He all the way from BC and is one of Bryan's babies. Widge is just a suck. He used to squeak and squeal when put on his back. Now he screams. I guess I didn't pay enough attention to the quieter sounds. :lol: I tend not to do it to him very often because I know it upsets him.