The following quotations helped me when I learned about a book that had a similar storyline to my work-in-progress and panicked, wondering whether I should continue writing:
Originality can come only from what you bring of yourself to your story. In other words, originality is not a function of your novel; it is a quality in you.
He follows that with:
Finding the power buried in your novel is not about finding its theme. I would say, rather, that it is about finding you: your eyes, experience, understanding and compassion. Ignore yourself and your story will be weak.
This resonates with me because it reminds me that I have to put myself into my writing. I'm not just telling a story--I'm telling a story that means something to me. That is what makes it unique.