So, at some point there was someone who came up with the very first knock-knock joke. Someone at some point wrote the very first mystery. But how many thousands of years have humans been around telling stories and eventually writing them down? It is not impossible that you might still stumble upon something that has never been told before, but the chances are ridiculously small at this point.
However, we still love to listen to and read stories. Even if it is vaguely like something else. In fact, chances are if it's like something else that we like we'll be even more interested. And, while there may come a point where not only are there no new stories to tell but all the possible variations ever have already been told, but I don't think that's happening anytime soon.
Every storyteller brings something slightly different to the table in terms of experience and perspective and language and goals. And, on a sentence level, certain things sound better to us. (This is why songs written in the key of D Major are so prevalent - not only is it a median range, but it sounds good to us.) It is natural to mimic those things which stick with us. (And, unless you are producing something verbatim, that's not really a problem.)
Best of luck with your book.