Here is an intro about matrix https://optics.ansys.com/hc/en-us/articles/360034929613-matrix-Script-command

Since this is a 2D matrix, you can access it as

neffTM=M(n,2);

neffTE=M(n,3)

where n is the index for fill factor., eg, n=1

you have the first value of the fill factor M(1,1); and neffTM and neffTE are the correspodent neff for this fill factor.

Please try and compare your original data.