It happens. One thing you can do is take it as a good sign that you were onto a trend. Using that state of mind, can you predict the next trend and beat other designers to the market?
I iterated on a dog show game for a few months with friends before shelving it. A few years later I played a dog racing game at Gencon and in the same weekend one of my playtesters sent me a photo from a Target store with a different, mass market Dog Show game!
I think the best thing you can do is work on finishing your game and make it the best you can. If you can find a way to add a unique mechanic there’s still room to innovate. Look at all the social deduction, take that or zombie games.