moving a curve by inverse slope of each point without overlap

Question

I am trying to draw curves a specified distance away from a curve. Kind of like the sides of roads are always a set distance away from the yellow lines in the center. I have code to do this, however, when done using my code it ends up with overlap in one of the curves.

Here is my code:

for (int i = 0; i < curves.Count; i++)
        {
            for (float j = 0; j < 1; j += .001f)
            {
                Vector2 temp = Vector2.CatmullRom(curves[i].Points[0], curves[i].Points[1], curves[i].Points[2], curves[i].Points[3], j);
                if (mid.Count != 0)
                {
                    if (temp != mid[mid.Count - 1])
                    {
                        mid.Add(temp);
                    }
                    else Console.WriteLine(temp == mid[mid.Count - 1]);
                }
                else mid.Add(temp);
            }
        }

for (int i = 0; i < mid.Count; i++)
        {
            if (i == 0)
            {
                Vector2 slope = mid[i] - mid[i + 1];
                double x = mid[i].X + (12 * Math.Cos(Math.Atan(-(slope.X / slope.Y)))),
                    y = mid[i].Y + (12 * Math.Sin(Math.Atan(-(slope.X / slope.Y))));
                side1.Add(new Vector2((float)x, (float)y));

                x = mid[i].X - (12 * Math.Cos(Math.Atan(-(slope.X / slope.Y))));
                y = mid[i].Y - (12 * Math.Sin(Math.Atan(-(slope.X / slope.Y))));
                side2.Add(new Vector2((float)x, (float)y));
            }
            else if (i < mid.Count - 1)
            {
                Vector2 slope1 = mid[i] - mid[i - 1],
                    slope2 = mid[i + 1] - mid[i];

                Vector2 slope = (slope1 + slope2) / 2;

                double x = mid[i].X + (12 * Math.Cos(Math.Atan(-(slope.X / slope.Y)))),
                    y = mid[i].Y + (12 * Math.Sin(Math.Atan(-(slope.X / slope.Y))));
                side1.Add(new Vector2((float)x, (float)y));

                x = mid[i].X - (12 * Math.Cos(Math.Atan(-(slope.X / slope.Y))));
                y = mid[i].Y - (12 * Math.Sin(Math.Atan(-(slope.X / slope.Y))));
                side2.Add(new Vector2((float)x, (float)y));
            }
            else
            {
                Vector2 slope = mid[i] - mid[i - 1];

                double x = mid[i].X + (12 * Math.Cos(Math.Atan(-(slope.X / slope.Y)))),
                    y = mid[i].Y + (12 * Math.Sin(Math.Atan(-(slope.X / slope.Y))));
                side1.Add(new Vector2((float)x, (float)y));

                x = mid[i].X - (12 * Math.Cos(Math.Atan(-(slope.X / slope.Y))));
                y = mid[i].Y - (12 * Math.Sin(Math.Atan(-(slope.X / slope.Y))));
                side2.Add(new Vector2((float)x, (float)y));
            }
        }

And here is a photo of the result: Curves with overlap

Any and all help would be appreciated.