YANBU, wear whatever protection you want to, it can't do any harm and may help keep you safe (but you'd still need to keep a safe distance and wash hands when you return home).
Also, when removing the mask after use, be aware that it could be quite germ ridden, so you probably need to wash/wipe it down regularly, just in case.
I just started a thread about a man who coughed his way around the supermarket today, so YADNBU.