Off hand it looks pretty good, I don't know what software you are using, but you could consider adding some light wrap. slightly shrinking the mask, adjusting the levels of the alpha channel to make a cleaner key, and adding a holdout mask to prevent the keyer from affecting the rest of the image.
The biggest issue is that the angle of the computer does not match the perspective of the onscreen stuff. To fix this you need to add a perspective warp/four corner filter, or if you are using a software with 3D compositing (HitFilm, Blender, etc...) simply adjust the screen layer in 3D space to match the angle of the screen.
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