Decreasing the size of a matrix in latex (overleaf)

I have this code in latex (overleaf to be precise) and it displays the image below. I used \footnotesize to decrease the size so it would fit on the width of the page however, it did not decrease enough. How can I reduce the size of the matrix more? Thanks!

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{multicol}
\usepackage{amsmath} 
\usepackage[a4paper, total={6in, 8in}]{geometry}

\title{example stackoverflow}
\author{cristian cotovanu}
\date{November 2022}

\begin{document}

\maketitle

\section{Introduction}
\subsubsection*{3)}
$\frac{1}{h_x^2} = 0.16$, $\frac{2}{h_x^2} = 0.32$, $\frac{1}{h_y^2} = 0.64$, $\frac{2}{h_y^2} = 1.28$. These values will be substitute in the matrix for more clarity.
\begin{equation}
\footnotesize
    \begin{bmatrix}
0.32 + 1.28 & -0.16 & 0 & -0.64 & 0 & 0 & 0 & 0 & 0\\
-0.16 & 0.32 + 1.28 & -0.16 & 0 & -0.64 & 0 & 0 & 0 & 0\\
0 & -0.16 & 0.32 + 1.28 & 0 & 0 & -0.64 & 0 & 0 & 0\\
-0.64 & 0 & 0 & 0.32 + 1.28 & -0.16 & 0 & -0.64 & 0 & 0\\
0 & -0.64 & 0 & -0.16 & 0.32 + 1.28 & -0.16 & 0 & -0.64 & 0\\
0 & 0 & -0.64 & 0 & -0.16 & 0.32 + 1.28 & -0.16 & 0 & -0.64\\
0 & 0 & 0 & -0.64 & 0 & 0 & 0.32 + 1.28 & -0.16 & 0\\
0 & 0 & 0 & 0 & -0.64 & 0 & -0.16 & 0.32 + 1.28 & -0.16\\
0 & 0 & 0 & 0 & 0 & -0.64 & 0 & -0.16 & 0.32 + 1.28\\
    \end{bmatrix}
\\
    \begin{bmatrix}
u_{1, 1}\\
u_{2, 1}\\
u_{3, 1}\\
u_{1, 2}\\
u_{2, 2}\\
u_{3, 2}\\
u_{1, 3}\\
u_{2, 3}\\
u_{3, 3}\\
    \end{bmatrix}
=
    \begin{bmatrix}
f_{1, 1}\\
f_{2, 1}\\
f_{3, 1}\\
f_{1, 2}\\
f_{2, 2}\\
f_{3, 2}\\
f_{1, 3}\\
f_{2, 3}\\
f_{3, 3}\\
    \end{bmatrix}
\end{equation}

\end{document}

Solution

One possibility would be to use an even smaller font size like \tiny.

However in this particular case, in which only the long entries on the diagonal force the columns to be rather broad, one might get away with a negative colsep:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{multicol}
\usepackage{amsmath} 
\usepackage[a4paper, total={6in, 8in}]{geometry}

\title{example stackoverflow}
\author{cristian cotovanu}
\date{November 2022}

\usepackage{tabularray}
\UseTblrLibrary{amsmath}

\begin{document}

\maketitle

\section{Introduction}
\subsubsection*{3)}
$\frac{1}{h_x^2} = 0.16$, $\frac{2}{h_x^2} = 0.32$, $\frac{1}{h_y^2} = 0.64$, $\frac{2}{h_y^2} = 1.28$. These values will be substitute in the matrix for more clarity.
{
\footnotesize
\begin{equation}
    \begin{+bmatrix}[
      colspec={@{~}ccccccccc@{~}},
      colsep=-2pt
    ]
0.32 + 1.28 & -0.16 & 0 & -0.64 & 0 & 0 & 0 & 0 & 0\\
-0.16 & 0.32 + 1.28 & -0.16 & 0 & -0.64 & 0 & 0 & 0 & 0\\
0 & -0.16 & 0.32 + 1.28 & 0 & 0 & -0.64 & 0 & 0 & 0\\
-0.64 & 0 & 0 & 0.32 + 1.28 & -0.16 & 0 & -0.64 & 0 & 0\\
0 & -0.64 & 0 & -0.16 & 0.32 + 1.28 & -0.16 & 0 & -0.64 & 0\\
0 & 0 & -0.64 & 0 & -0.16 & 0.32 + 1.28 & -0.16 & 0 & -0.64\\
0 & 0 & 0 & -0.64 & 0 & 0 & 0.32 + 1.28 & -0.16 & 0\\
0 & 0 & 0 & 0 & -0.64 & 0 & -0.16 & 0.32 + 1.28 & -0.16\\
0 & 0 & 0 & 0 & 0 & -0.64 & 0 & -0.16 & 0.32 + 1.28\\
    \end{+bmatrix}
    \begin{+bmatrix}
u_{1, 1}\\
u_{2, 1}\\
u_{3, 1}\\
u_{1, 2}\\
u_{2, 2}\\
u_{3, 2}\\
u_{1, 3}\\
u_{2, 3}\\
u_{3, 3}\\
    \end{+bmatrix}
=
    \begin{+bmatrix}
f_{1, 1}\\
f_{2, 1}\\
f_{3, 1}\\
f_{1, 2}\\
f_{2, 2}\\
f_{3, 2}\\
f_{1, 3}\\
f_{2, 3}\\
f_{3, 3}\\
    \end{+bmatrix}
\end{equation}

\end{document}