nut was wrong size...it happens... derailer, single speed, speed hubs all have different nuts....i would do something unorthodox but it should work...

if you just got to twist it twice you can force it out and sand the damage threads...go to a bike shop and get nuts that really fit...

but before you try a new nut you NEED to clean (eliminate) the damaged thread...its tricky but can be done...

pics would be really usefull...