Do you need to consolidate the meaning of Third Conditionals? Here's a worksheet which practice the meaning and form of Third conditional if clauses. It asks students to make up sentences according to the given situation. It's an ideal worksheet which only focuses on type 3 if clauses and can accompany a lesson after the grammar presentation stage.
Be careful at the seventh exercise of the worksheet. It uses "prepared" as an adjective which may confuse students with the past simple verb form. Consequently, they should use "had been prepared" in the answer which is also confused as a passive form.
encourage peer review in the feedback stage
I strongly suggest you to encourage peer review in the feedback stage. Each exercise can have a different answer from the answer key. When students check each other's answers, there'll possibly be more room for discussion and student will get more of this worksheet.