Paper [topic-は] conclusion [object-を] leaving, rest [topic-は] is-completed.
残し is the continuative form (連用形) of 残す ('to leave behind'), used to chain clauses. 仕上がっている uses intransitive 仕上がる ('to be completed') rather than transitive 仕上げる. The は after あと contrasts 'the rest' with 'the conclusion.'