Mis- (wrongly, badly)
Mis-
Wrongly or badly.
Arjun misread the bus number and reached the wrong stop.
Misspell
To spell a word wrongly.
Many people misspell 'necessary' in their notes and messages.
Misunderstand
To get the wrong meaning.
Please don't misunderstand me; I liked your idea.
Remember: mis + spell = misspell, with double s. It is a famous trap: the word 'misspell' is itself often misspelt!