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I'm glad you liked the ending. I don't know what is missing in the fluency since the beginning ended with a knock at the door, and my ending began with the same character opening the door. In terms of plot it doesn't get more fluent and seamless than that.

But did you mean in terms of style perhaps? I definitely didn't make an attempt to keep the style the same, and I endeavored to make the tone more sinister and frightening. If you're willing to give more specific feedback I'd like to hear it. I can always learn more!

Many times when I read the stories that have the beginning of an author but the continuation of another author caught a narrative leap. It is logical that this happens because they wrote two different people.
Regarding your continuation of the story, I feel that the narrative link is forced. For that reason your story at the beginning is not fluent because it seeks to adapt to the elements that you want to place in the end and at the same time to the elements that the obligatory drama has. It is my humble opinion.
If I read only your story, I would tell you that it is perfect.