when the bmap is 1920x1080 write the fuction:

void splash_switch()
{
while(1)
{
wait(1);
gamepanel.scale_x = screen_size.x / 1920;
gamepanel.scale_y = screen_size.y / 1080;
wait(1);
}
}

and write in the main:

...
level_load("game.wmb");

wait(1);

splash_switch();
}