Mispeak or Misspeak: How To spell?
The word Mispeak is misspelled against Misspeak, a verb meaning "To err in speaking."
Misspeak has double "ss" is mispronounced as "s"Remember double 'SS' in between the strings mi & peak which should not be misspelled with single 'S'
Wrong Spelling:  mi-s-peak  Correct Spelling:  mi-ss-peak 
Find more wrongly spelled words of Misspeak to spell it well.