Please do not panic. If the band is small, it is more than likely to pass through. Make sure he carries on eating and drinking and add more fibre to his diet to help get his gut moving. Watch out for signs of a puffed up coat, decreased activity and straining to poo for the next 3 days and if you are concerned at all, seek veterinary advice asap.
Whatever you do, don't feel bad. My own piggies have managed to get hold of things they shouldn't have done.