tikz 图片的水平范围：为什么它被截断？

Question

这是我的代码：

\documentclass[border=2pt]{standalone}
\usepackage{pgfplots}

\begin{document}
\[
\begin{tikzpicture} [scale=1]
\begin{axis}[
             axis x line = center,
             axis y line = center,
             xlabel=$x$,
             ylabel=$y$,
             xtick={-2.0,-1.0,0.0,1.0,2.0},
             xticklabels={$-2$,$-1$,$0$,$1$,$2$},
             ytick={-2.0,-1.0,0.0,1.0,2.0},
             yticklabels={$-2$,$-1$,$0$,$1$,$2$},
             domain=-2:2,
             grid=none, 
             unit vector ratio*=1 1,
             enlargelimits = true
            ]
 \foreach \n in {0.5,1,1.5,2,2.5,3}
  {
   \addplot[
            thick,
            variable=\t, 
            domain=-3:3, 
            samples=200, 
            color=blue
           ] 
            ({\t}, {\t^2/(2*\n^2) - \n^2/2});
 }
 \foreach \m in {0.5,1,1.5,2,2.5,3}
  {
   \addplot[
            thick,
            variable=\t, 
            domain=-3:3, 
            samples=200, 
            color=red
           ] 
            ({\t}, {\m^2/2 - \t^2/(2*\m^2)});
 }
\end{axis}
\end{tikzpicture}
\]

以下是我得到的结果：

为什么会这样？我该如何解决？