Translation:Everyone has arrived, where are you now?
Actually it is correct. I'm afraid that Duolingo perceives "everyone's" as "everyone is" instead of "everyone has" :(.
If you hover over them you can see that "现在" (as a compound) = "now / right now". While "在" alone = "is located". So literally: 你 (you) 现在 (right now) 在 (are located) 哪儿 (where). Mandarin has lots of compound words that have different meanings than the characters they're made of.