\chemleft bracket too far from molecule

Question

I am trying to draw a reaction scheme in chemfig, but the chemleft bracket is too far away from the actual molecule and I do not know why. My code looks like this:

\documentclass{article}
\usepackage{tikz}
\usepackage{chemfig}

\begin{document}
\setchemfig{cram width=3pt}
\schemestart
\subscheme{
\chemleft[
    \chemfig{@{F}\Lewis{0:2:4:6:,F}}
\chemright]}
\+
\chemfig{F-@{B}{\phantom{B}}(-[2,0,,,draw=none]{})(<[:-20]F)<:[:20]F}
\arrow{->}
\chemleft[
    \chemfig{\chembelow[0.5pt]{F}{\scriptstyle\hspace{4.5mm}\oplus}-[@{cb}:-90,0.8]\chemabove[0.5pt]{B}{\scriptstyle\hspace{4.5mm}\ominus}(<:[:-40,0.8]F)(<[:-70,0.8]F)-[:-140]F}
\chemright]
\schemestop
\tikz[overlay,remember picture]{
\begin{scope}[overlay,shift={(B)}]
\draw[-] (-0.1,0.2) ..controls +(120:1) and +(60:1) .. (0.1,0.2);
\draw[-,fill=black!10] (-0.1,-0.2) ..controls +(-120:1) and +(-60:1) .. 
+(0.2,0);
\end{scope}
\node[fill=white,inner sep=0.1pt] at (B){{\fontfamily{cmr}\selectfont
B
}};
\draw[-latex,shorten <=2pt] (F) ..controls +(90:1.7cm)and+(90:1cm)..
([yshift=9pt]B.north);
\draw[-latex,densely dashed] (cb) arc (270:180:0.7 and 1) node[above=0.15cm,align=center] {\scriptsize coordinate \scriptsize covalent\\ \scriptsize bond};
}
\chemmove{\node[xshift=5pt] at (c2.north east) {$-$};}
\chemmove{\node[xshift=5pt] at (c3.north east) {$-$};}
\end{document}

Here is the output which illustrates my problem As you can see, the left [ (chemleft[) braces are placed at some distance from the actual molecule. How do I fix this?