Moving mouse quickly doesn't create the points in Red like when moved slowly why ?

On top of form1 i did:

private int pixelscounter;
private int counter;
private float xFactor, yFactor;
List<PointF> points = new List<PointF>();
double increment = 1.25;
double factor = 1.0;
Image img;
private Point startingPoint = Point.Empty;
private Point movingPoint = Point.Empty;
private bool panning = false;
GraphicsPath gp = new GraphicsPath();
GraphicsPath redgp = new GraphicsPath();

In pictureBox1 move event i did:

if (checkBox2.Checked && e.Button == MouseButtons.Left)
{
    gp.AddLine(e.X * xFactor, e.Y * yFactor, e.X * xFactor, e.Y * yFactor);
    pixelscounter += 1;
    if (pixelscounter == 10)
    {
        redgp.AddEllipse((e.X) * xFactor, (e.Y) * yFactor, 3f, 3f);
        pixelscounter = 0;
    }
    p = e.Location;
    pictureBox2.Invalidate();
}

In pictureBox2 paint event:

if (checkBox2.Checked)
{
    using (Pen pp = new Pen(Color.Green, 2f))
    {
        pp.StartCap = pp.EndCap = LineCap.Round;
        pp.LineJoin = LineJoin.Round;
        e.Graphics.DrawPath(pp, gp);
    }
    using (Pen pp = new Pen(Color.Red, 2f))
    {
        pp.StartCap = pp.EndCap = LineCap.Round;
        pp.LineJoin = LineJoin.Round;
        e.Graphics.DrawPath(pp, redgp);
    }
}

What I did is that when I click mouse left button press without leave it then drag the mouse around pictureBox1 its drawing a line in pictureBox2 in green and every 10 locations(pixels) its creating a red point automatic.

The problem is when I move the mouse fast or fast movements then the red points are not in the same distance of 10 locations(pixels) if I move the mouse very very slow the red points are too close to each other if I move the mouse regular more or less it seems that the points distance between each other are ok and if I move the mouse fast/very fast the distance between every red point is large more then 10 pixels.

How can I fix/solve this mouse movements problem ?

Can someone show me in my code the fixed code how to calculate the difference between the start and the current position. Then draw a dot for every 10 pixels in between and set the new start position on the last dot i added ?

I saw the formula but not sure how to do it in my code.