why caption is not centered under figure when using forest? How to correct

Question

I am following an answer in How to include caption in \begin{forest}...\end{forest} in LaTex where it shows how to put forest inside figure with caption, under the part where it says

If you want a caption, switch to article and put the tree in a figure.

But when I try it on my code, in TL 2022, the caption is not exactly in the center. It seems to be shifted to the left. Here is a MWE and screen shot

\documentclass{article}

\usepackage{amsmath}
\usepackage[edges]{forest}
\usepackage{caption}%do I need this?

\begin{document}
\begin{figure}
\centering   
\fbox{\begin{forest}
for tree={
    draw, rounded corners, fill=blue!20,
    minimum height=1.5cm, minimum width=2cm,
    align=center, base=b,
    s sep=1cm, l sep=.5cm,
    if level<=2{edge=-latex}{edge=red},
}
[differential\\equation
    [first Order 
     ,calign=last
        [first order\\degree not One,
           [{\small goto\\figure 2}, circle,draw,fill=yellow!20, minimum width=1cm]
        ]
        [first order\\degree one, 
            [{\small goto\\figure 1}, circle,draw,fill=yellow!20, minimum width=1cm]
        ]
    ]
    [second order, calign=first
        [linear]
        [nonlinear]
    ]
    [higher order, fit=band]
]
\end{forest}}
\caption{Main flow chart for solving an ode}
\label{fig:main}
\end{figure}
\end{document}

Compiled using lualatex gives this

Is the above the correct way to put forest inside figure with frame with caption? How to make caption be centered? I am using \centering.

ps. I used \fbox to put frame around the figure. Not sure if this is the best way or not but it seems to work.

Answer 1

As commented by @daleif, you have a warning:

lilla.tex|35 warning| Overfull \hbox (84.20647pt too wide) in paragraph at lines 35--36

...and 84 points is quite a bit. I suggest using \overfullrule=5pt before \begin{document} always when editing a new document, which makes this kind of problem quite evident: