I once used a larger cut off wheel (don't remember the size) on a 4 1/2" grinder. I named it the meat slicer, and was very careful using it but realized it was Too dangerous to use like that so I took it off and quit doing that without getting hurt. I'm very lucky not to have had an incident, and recommend the simply wise safety mentioned above.
Heal up and DON'T DO THAT AGAIN!