just take another picture of your room, but stand where you were standing there and take a picture that is of what is “behind” the camers, then set that as your background or make a big plane with that image on it and see if you can get some reflections going. It’s only a little bullet, so really all you need is a little bit of reflection.
Also, you’ll need to work on the lighting, get a much more ambient glow, because at the moment the lighting of the bullet is completely different to the lighing on the picture. See those black bits around the edges of the models? There are no black bits around you in that picture.
Also, defocus the bullet a bit, not only will it fit into the image more, it will hide and small inaccuracies. Keep blending!