The parity bit in the bottom-right-hand corner (where the parityRow and parityColumn intersect) will be the same, regardless of whether you calculate it via the parityRow or the parityColumn.

So,

if your original matrix was 5x5, and the parity-augmented matrix is 6x6,
then
the bit at matrix[5][5] (remember zero-based counting!) can be calculated from matrix[0..4][5] OR matrix[5][0..4]. They will both turn out to be the same!

The proof for this is simple. See, if you can figure out why :-) [for bragging rights only]