-살찔까 봐 걱정돼.

I'm worried to get fat. --> I'm afraid I'll get fat.

=> Another way: Your sentence is okay and this is another way of saying it.

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-떠날 준비 다 했니?

Are you ready to leave? ✔

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-네, 엄마

Yes mom. --> Yes, Mom. (Punctuation)

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