Barry, a mask won't top you catching the virus. The mask is to stop you spreading it to other people if you have it. The mask stops you breathing virus out onto other people.
To avoid catching the virus, you need to stay a couple of meters away from other people, and don't let anyone breath on or near you. And wash your hands after being out in public and before you touch your face.
If you go out in public and are near people, then have a shower and change your clothes when you get home. It's also a good idea to wash keys and disinfect mobile phones and other items you have with you, when you are out in public.