Getting over the hang ups (over thinking)

One thing about writing that seems to hang me up is the idea of being "fresh" or "new" without being too removed from one's audience. I have my beta readers in line and a very short novel that I expect will need heavy revision

I'm currently fleshing out the last few chapters of the novel and have come upon a few major stumbling blocks. One is the niggling feeling that the literary device I'm using is contrived. Then, there's the idea that I'm doing something that feels like every fantasy writer before me has done it before. Or worse, the little voice in my head that says, "Didn't the ________ storyline do something similar?" 

Is this valid? Or am I just using this as another excuse to let the work sit?