Hackers Help: Expedit Help Needed

Expedit

I got to this next to last step assembling this shelving unit and the two screws won’t go in. I tried the screws in the other corner and they work there so the screw isn’t the issue. Does anyone know how big of a wood piece they put in the corners (see circle noted by ‘A’)? If it is big enough maybe I can put in my own screw(s) offset from the hole they have in there.