Hi Pelin, I'm not a language teacher, but as a native English speaker your second sentence sounds awkward. I would change it to "We didn't officially meet earlier".
Perhaps this is because "earlier" is a more specific time than "before". "Earlier" makes it sound like you meant earlier that day, or earlier during that specific event.
Again, I'm not a language teacher, so I can't share specific grammar rules.
Your other sentences look great!