I'm currently transitioning from C#/XNA to C#/OpenTK but I'm getting stuck at the basics.

So I have this Sprite-Class:

public static bool EnableDebugDraw = true;
public float X;
public float Y;

public float OriginX = 0;
public float OriginY = 0;

public float Width = 0.1f;
public float Height = 0.1f;

public Color TintColor = Color.Red;
float _layerDepth = 0f;

public void Render()
    {
        Vector2[] corners =
        {
            new Vector2(X-OriginX,Y-OriginY), //top left
            new Vector2(X +Width -OriginX,Y-OriginY),//top right
            new Vector2(X +Width-OriginX,Y+Height-OriginY),//bottom rigth
            new Vector2(X-OriginX,Y+Height-OriginY)//bottom left
        };
        GL.Color3(TintColor);
        GL.Begin(BeginMode.Quads);
        {
            for (int i = 0; i < 4; i++) GL.Vertex3(corners[i].X,corners[i].Y,_layerDepth);                             
        }
        GL.End();

        if (EnableDebugDraw)
        {
            GL.Color3(Color.Violet);
            GL.PointSize(3);
            GL.Begin(BeginMode.Points);
            {
                for (int i = 0; i < 4; i++) GL.Vertex2(corners[i]);
            }
            GL.End();

            GL.Color3(Color.Green);
            GL.Begin(BeginMode.Points);
            GL.Vertex2(X + OriginX, Y + OriginY);
            GL.End();
        }

With the following setup I try to set the origin of the quad to the middle of the quad.

_sprite.OriginX = _sprite.Width / 2;
_sprite.OriginY = _sprite.Height / 2;

but this sets the origin to the upper right corner of the quad, so i have to

_sprite.OriginX = _sprite.Width / 4;
_sprite.OriginY = _sprite.Height / 4;

However this is not the intended behaviour, could you advise me how I fix this?