「わたし」　と　「あたし」　ちがいはなんですか。
Both has the same meaning but is it different in saying to friends and families to company bosses??? [Recently, I watched dozens of Japanese movies where I heard あたし　the most!!!]
ありがとうございました。

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Answer

In oral
わたしand あたし  same meaning. 
わたし is slightly politer than あたし.
わたくし is the politest.

to company bosses, I say わたし or  わたくし
to friends and families, I pronaunce わたし or あたし. it's casual.
 
but men hardly pronaunces あたし. it's strange.
When the male says  わたし or  わたくし, It's　polite.
Casual way for men, おれ（俺） or ぼく（僕）.

In written
私(watashi or watakushi)　is correct　and formal.
わたし is not wrong, It's casual.
あたし is informal and a little childish.

I hope my response is useful for you.

Answer

Thank you!!!
You previously asked me to fix your English if there is any mistake so instead of "You've already get a perfect answer"
 it will be 
"You've already GOT a perfect answer"...^_^

Answer

You've already get a perfect answer.