Call and apologize and move on with your day. As others have pointed out, day 4 is still very early. The forgetfulness is part of the process and shows your brain is rewiring itself and repairing. So, as annoying as it is, the forgetfulness is usually a good sign things are improving so try to look at the bright side. In my first few weeks back to being sober, I made my assistant at work remind me of EVERYTHING. I needed it or I would forget (thank goodness she is a patient person!). I even forgot my dad's birthday for the first time ever. That sucked. But then the fog started to lift and it got better. Hang in there and keep up the good work!