Greetings!
I have submitted my 500 words college essay on a subject that turned out to be exactly the same as one on which a book is based. I would like to know if this could hurt my chances in any way.
Thank you
There are millions of books in this world. Indeed, it is highly likely that any story one comes up today with has a book based on it.
Frankly speaking, I wouldn’t worry about it if the book were just a random book. But if it is a popular series like Dan Brown’s or maybe some popular classic like Jane Eyre’s then there is reason to worry. Although the chances of the admissions staff reading the exact same book you talk about are too less, the more popular the book, more the chances.
Now, if you have genuinely written the essay, I think they’ll know. Maybe you’re just fretting about it.
In any case, there is absolutely nothing you can do about it. Just wait till the decision date. And in the meantime, remember, you are not in a bad position. Everything will be alright 
One time, I had to represent my district in a fight to the death…
Well, the author 450 ratings and only 67 reviews in goodreads… that is not so bad, I assume.