You could try cleaning the screen. Use a good quality Q-tip, distilled water (moistened only). Go in through the lens mount - removing C220 screens is not recommended unless you are prepared for the shims that will fall out.
Ambient light is a problem. You really need to use the magnifier to focus, even if you frame at arm's length. You also need to check that the magnifier is suitable for your eyesight. If you cannot focus the rim of the focus spot correctly, you will never bring the image to focus.