Jesus saying “It is finished” has nothing to do with prophecy. He was referring to his sacrifice for the sins of the world. Yes, the disciples were looking for “the end of the age” in their lifetimes, but they were wrong.
You are correct concerning, “It is Finished!”, he had yet to come in judgement upon Israel. Remember, John had told them he baptized only with water, but the one to come would baptize with water and fire - the fire was yet to com.
The disciples were not wrong - they just believe what Jesus had told them. Imagine that!