The latter one is also accepted but i don't think it's widely accepted in formal writing. True, accidentally is the correct spelling. On the other hand, middle english used accidentlych as an adverb, and this would produce accidently in modern english.
Imp The Mischievous Mythical Creature Mythical Encyclopedia
So the regular construction would be accidentally. In a word, intentionally or accidentally? Does this sentence mean 'you' intentionally tried to hurt 'yourself' or accidentally hurt 'yourself'?
The jury returned a verdict of accidental death 陪审团.
Accidentally：没有附带性；完全出乎意料。 例句：i accidentally broke a glass. Dumbtionary (a dictionary of misspelled words).
