5 立体中tikz画圆变成了椭圆

'''documentclass[border=2pt]{standalone}
usepackage{amsmath,amssymb}
usepackage{tikz}
usepackage{tkz-euclide}
usetikzlibrary{math,calc,intersections,through,angles,arrows.meta,shapes.geometric,shadows,quotes,spy,datavisualization,datavisualization.formats.functions,plotmarks}
tikzset{every picture/.style={samples=300,smooth,line join=round,font=small,thick,>={Stealth[]}}}
begin{document}
begin{tikzpicture}[scale=2,

x={(-.4cm,-.4cm)},
y={(1cm,0cm)},
z={(0cm,1cm)}
]
 \tikzmath{\r=.1;}
\coordinate[label=45:$D$](D)at(0,0,0);
 \coordinate[label=below:$A$](A)at(1,0,0);
 \coordinate[label=right:$C$](C)at(0,1,0);
 \coordinate[label=below:$B$](B)at(1,1,0);
 \coordinate[label=left:$A_1$](A1)at(1,0,1);
 \coordinate[label=right:$C_1$](C1)at(0,1,1);
 \coordinate[label=above:$B_1$](B1)at(1,1,1);
 \coordinate[label=above:$D_1$](D1)at(0,0,1);
 \coordinate[label=left:$E$](E)at($(D)!.5!(A)$);
 \coordinate[label=right:$F$](F)at($(B)!.5!(C)$);
 \coordinate[label=above:$O$](O)at(.5,0.5,0.5);
 %\tkzDrawPoints(O);
 \filldraw[cyan](O)circle(\r);
 %\coordinate[label=left:$M$](M)at($(A1)!.5!(D)$);
 %\coordinate[label=right:$N$](N)at($(B)!.5!(C1)$);
 \draw(A1)--(B1)--(C1)--(D1)--cycle (A1)--(B1)--(B)--(A)--cycle (B1)--(C1)--(C)--(B)--cycle;
 \draw[dashed](D1)--(D)--(A) (C)--(D);
 \draw[cyan,dashed] (A1)--(E)--(F)--cycle ;
 \draw[cyan](B1)--(F);
 \draw[red,dashed](A1)--(C);
\end{tikzpicture}

end{document}yuan.tex
'''
用tkz画圆是可以的，但在tikz中圆变成了椭圆，tikz命令中如何让这个椭圆恢复为圆？谢谢！

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