Is he saying down, or done? I'm hearing done, and it makes more sense with the theme of the song. "I'm so down x3... toooday" Really gives us no context to what exactly he is, "down" to. However, if you read the lyric as, "I'm so done x3.... tooooday" it follows the theme of the song, with context from prior lyrics, as well as fitting the title of the song itself.