It appears that you generated just one row of the desired 18 x 18 matrix. Why not generate a row of 18*18=324 complex numbers and then partition the result into a matrix? Something like this slight modification to your code should work.

datos = Partition[
   Riffle[RandomVariate[NormalDistribution[], 18^2], 
    RandomVariate[NormalDistribution[], 18^2]], 2];

Partition[Apply[Plus, {#[[1]], #[[2]]*I} & /@ datos, 1], 
  18] // MatrixForm

You can probably simplify a bit. For example, since real and imaginary parts are taken from the same normal distribution, you could generate all the randoms at once, and then partition to make the next step a bit simpler. Something like the following might be a bit faster.

datos = Partition[RandomVariate[NormalDistribution[], 2 18^2], 18^2];

Partition[datos[[1]] + I datos[[2]], 18] // MatrixForm