PGFPLOTs incomplete grid, missing minor grid from both up and right sides

I am making a file with pgfplot package and I want the grid to be with minor grids line complete from both sides, this is my trial:

\documentclass{standalone}

\usepackage{filecontents}
\usepackage{amsmath}
\usepackage{tkz-euclide}
\usepackage{makecell}
\usepackage{ifthen}
\usepackage{pgfmath}

\usetikzlibrary
{
    intersections, decorations.markings, angles,
    quotes, calc, arrows, arrows.meta,shapes.geometric
}

\usepackage{tikz-3dplot}

\usetikzlibrary{calc,intersections,arrows.meta}
\usepackage{hyperref}

\usepackage{tikz,tikzscale}
\usepackage{chemfig,chemformula}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\usepgfplotslibrary{fillbetween}

\begin{document}
    

    \begin{filecontents}[overwrite]{fig2.tikz}
            \begin{tikzpicture}
                    
                    
                    
                    \pgfplotsset{
                            tick label style = {font = {\fontsize{11.25}{14}\selectfont}},
                            label style = {font = {\fontsize{11.25}{14}\selectfont}},
                            legend style = {font = {\fontsize{11.25}{14}\selectfont}},
                    }
                    
                    
                    \pgfplotsset{
                            outer axis line style={thick,},
                            grid = both,
                            tickwidth = 0.25cm,
                            set layers,
                    }
                    
                    
                    
                    \begin{axis}[anchor=origin,
                    grid=both,
                            grid style={thin, draw=gray!20},
                            major grid style={thin,draw=gray!50},
                            minor x tick num={3},
                            minor y tick num={4},
                            minor tick length=0pt,
                            xmin=-4,xmax=4,
                            ymin=-16,ymax=4,
                            xlabel={$x$},
                            xlabel style={at={(ticklabel* cs:1)},anchor=west},
                            ylabel={$y$},
                            ylabel style={at={(ticklabel* cs:1)},anchor=south},
                            xtick={-3,...,3},
                            tickwidth=0.25cm,
                            major tick style={black,thick},
                            extra x ticks={-4,0,4},
                            extra x tick labels={,0,},
                            extra x tick style={grid=both,black,
                                    major tick style={draw=none},
                                    tick label style={anchor=north east,xshift=-.5*\pgfkeysvalueof{/pgfplots/major tick length}},},
                            ytick={-14,-12,...,2},
                            extra y ticks={-16, 4},
                            extra y tick style={grid=both,major tick style={draw=none},},
                            extra y tick labels={},
                            axis lines=middle,
                            scale only axis,
                            axis line style={>={Stealth[scale=1.2]},<->,thick},
                            samples=1000]
                            
                            \addplot[domain=-4:4,draw=red,draw opacity=0.1,fill=red,fill opacity=0.1] {(3*x-2)*(x+3)}--(4,4)--(4,-16)--(-4,-16)--(-4,4)--cycle;
                            \addplot[domain=-4:4,draw=red,dashed] {(3*x-2)*(x+3)};
                            
                    
                    \end{axis}  
                    
                    
            \end{tikzpicture}
    \end{filecontents}
    
    \includegraphics[width=\linewidth]{fig2.tikz}
\end{document}