GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it
#g1 f2 z2 n1 c2 2x 2 0 -1 1 0 2x 2 1 0 0 1 2x 2 0 1 -1 0 2x2 % zentr 0 -1 1 0 2x2 % zentr -1 0 0 -1 2x2 %normalizer 0 1 1 0 2x2 %cen 0 -1 1 0 2x2 %cen -1 0 0 -1 2^2 = 4 %order of the group