End of story:没什么可说(或做)的了,到此为止 used when you are stating that there is nothing more that can be said or done about sth

Look, I told you I can't give you a job here. End of story.
听着,我跟你说了我没法在这里给你安排工作,不要再说了.

Not be the end of the world:not be a disaster 不是世界末日,没有那么糟糕

It wouldn't be the end of the world if you couldn't get into college. I'm sure you'd be able to find a good job anyway.
不能上大学又不是世界末日,我相信你总能找到一份好工作的.

Why are you so upset? It's not the end of the world.
你干嘛这么难过?这又不是世界末日.