I mean, the stylistic rules of when to use commas, etc. vary between languages. When you use "that" in English, you shouldn't include the comma (but Duolingo for the most part is punctuation blind as far as I know).
I have used up all the words in the correct order and it still says im missing a word then says the correct translation is what i said. Im not on the free-typing exercise yet so i cannot put commas or quotation marks. Is this a bug?