Thank you for writing.
You can control the width of the ScatterLineSeries through the BorderWidth property:
ScatterLineSeries scatterLine =
scatterLine.BorderWidth = 5;
To change the font of the legend elements you can iterate them and change their font using the following code:
Font font =
, 16, FontStyle.Strikeout);
item.Font = font;
I hope this is useful. Should you have further questions, I would be glad to help.