Compute parity matrix in $GF(3)$

Question

I want to compute the control matrix/parity matrix $H$, when given a generating matrix $G$ for a linear code in $GF(3)$:

G = \begin{bmatrix} 2 & 1 & 1 & 1 & 0 & 0 \\ 1 & 2 & 1 & 0 & 1 & 0 \\ 1 & 1 & 2 & 0 & 0 & 1 \\ \end{bmatrix}

I am aware that the matrices have the following structure:

$G = [I|P]$

$H = [-P^T|I]$

My questions are the following:

1. Do I have to bring $G$ in canonical form first, aka have the identity matrix on the left? Because currently, I and P are basically on the wrong sides.

2. I know that when transposing $P$ to $-P^T$ in $GF(2)$ the values are essentially unchanged, aka $-0$ is still $0$ and $-1$ is $1$. But how is this in $GF(3)$? What is $-0$,$-1$ and $-2$? They are different, right?