楕円のスタイルは幅広くカスタマイズできます

ScottPlot.Plot myPlot = new();

var circle = myPlot.Add.Circle(center: Coordinates.Origin, radius: 5);
circle.LineStyle.Width = 5;
circle.LineStyle.Pattern = LinePattern.Dashed;
circle.LineStyle.Color = Colors.Green;
circle.FillStyle.Color = Colors.Navy;
circle.FillStyle.HatchColor = Colors.Red;
circle.FillStyle.Hatch = new ScottPlot.Hatches.Striped();

myPlot.Axes.SetLimits(-10, 10, -10, 10);

myPlot.SavePng("demo.png", 400, 300);