Lots of stories have already been told. Depending on how far you reduce them, either ALL of the stories have already been told, or we will NEVER be able to tell all the stories, even if we gave infinite marmosets infinite typewriters.
"NO, MY BOOK IS NOT 'JUST LIKE HARRY POTTER.'"
We all want to write unique stories, and there's nothing quite so crushing as telling someone your idea only to be told that it sounds 'just like' something else, even if that something else is wonderful. Even being told to pitch your book as "popular thing meets other popular thing" can feel a little cringey. This is your story, damn it. It's special and one of a kind and all of those other things you doubt at three in the morning.
BUT. There are two reasons you should not feel bad about comparisons, and I'm going to tell you both of them in case one doesn't do it.
Reason number one: Most people just haven't read that many books. If your 1920's story sounds just like The Great Gatsby to them, it might be because they know literally nothing else about the 1920's. They're saying the only thing they can think of. They're trying to relate. Pat them on the head, and move on with your life.
Reason number two: Nobody knows your book like you do, and until they read the whole thing, they're looking at it through a telescope. Depending on the length of your plot summary, it can be like trying to see Pluto through binoculars. OF COURSE it sounds like Interview with a Vampire to them. They only know three things about it: It's a book, with vampires, who wear fancy clothes. They're going to be very surprised when it turns out your vampires are working-class grunts in a modern-day orchestra.
Let's play a game: I recently purchased an object bigger than a breadbox. It has two wheels and a motor. It's red. It's loud. I would love to tell you all about it, but oops, I'm limited to sixty words. What is it?
Lock in your answers.
Now scroll down.
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Did you say motorcycle? Wheelbarrow? Do you see how the human tendency to extrapolate patterns makes them jump to conclusions?
This also applies to your story. So give yourself, your book, and your 'critic' a break.