nginx .conf redirect to 404.php

Question

have this .conf file to my website, but everytime it should redirect to 404 page it says file not found, however if it goes to a normal page it works always.

server {
    listen 80;
    server_name mywebsite.com;
    client_max_body_size 50M;
    root /var/www/html;
    index index.php index.html index.htm;
    location / {
        try_files $uri $uri/ @rewrite;
    }
    location @rewrite {
        rewrite ^/(.*)$ /$1.php last;
    }
    location ~ \.php$ {
        include fastcgi_params;
        fastcgi_pass php:9000;
        fastcgi_param SCRIPT_FILENAME /var/www/html/$server_name$fastcgi_script_name;
    }
    error_page 404 /404.php;
    location = /404.php {
        internal;
        include fastcgi_params;
        fastcgi_pass php:9000;
        fastcgi_param SCRIPT_FILENAME /var/www/html/$server_name/404.php;
    }
}

i just dont know why it says file not found, when i open the file directly http://mywebsite.com/404.php it works just fine