What do you mean by これ and でかったんです?

There is nothing wrong with you, and your translation is very authentic.

I want to make sure that this is for me.

You don't know if this is for you. You ask each other questions and want to know the answers.

According to the original translation, it is [this, is there any problem with sending it to me? ]

So if you translate according to the meaning, you translate. "Is this for me?"

これでかったんですね

This will completely change the meaning.

This is what you think should be sent to you, and you want the other party to agree.

This is addressed to me. No question mark. If translated into Chinese, the content is the same, but the meaning is completely different.

Please refer to ~