You have death anxiety and you're not alone in fearing dying.
https://en.wikipedia.org/wiki/Death_anxiety_(psychology)
It's not easy, but you have to try and live life and stop thinking about death all the time. I used to fear death all the time too when I was younger. But now I'm at peace with the fact that I'm gonna die someday.
Nobody really knows for sure what happens when you die. But I believe it will be like sleeping but you never wake up again.