You have got:
load z_matrix {
C12
C13 c12c13 1.4055394
N4 c12c13n4 132.409002
C8 c12c13c8n4 179.661007
}
Z-matrix should have one atom on the first line. Two on the second, three on the third and four onwards. In your description you have one atom on each line. My guess is that you want to write some space there. Topas uses the standard Z-matrix format except parameters can have names or equations. Best to have a look at z-matrix format; try
https://en.wikipedia.org/wiki/Z-matrix_%28chemistry%29