If you chased the threads with the appropriate tap you should be ok. Try rotating the spark plud CCW until you feel it fall into the start of the first thread, then go CW very slowly. This is a trick used on fine pitch threads.

Maybe add a slight amount of anti-seize to keep it from galling the existing threads worse.
Be carefull and good luck

 

I the threads are FUBAR then chasing it is just going to cut them up even worse. Any route you choose, be careful using your existing threads or helicoil. If that fails, time and $$ are going to go way up.