Well, I hate to say it but you didn't ask here before you blasted I guess. I for one would have told you DON'T DO IT!!!!
Sand blasting creates "It is totally ruined throw it in the trash" kinda damage. I hope I am wrong for your sake, I can say with certainty it will take someone who really knows this stuff to save them if they are very badly stretched.
Understand that each grain of sand acted as a little hammer spreading the molecules on the top surface of the metal apart. You have increased the size of the top layer of metal only.
A shrinking disc may be the only way a novice may be able to save them.