Mesh's corners are not where it's supposed to be

My goal was to make a Quad that would take up the entire screen, regardless of where the camera moved, or zoomed in/zoomed out. I changed the corners of the Quad's mesh to be the corners of the visible game area...but the top right and left corners aren't where they're supposed to be.

I even tried spawning a test game object in the top-right (the same top-right coordinate that the Quad uses) and it actually did show up in the corner, unlike the Quad.

Any ideas what's going on?

     Ray topLeft,topRight,botLeft,botRight; //Rays shot out from camera to figure out the 4 corners for viewRect
     float distance; //Used to find out how far camera is from xy plane 
     Vector3 tl,tr,bl,br; //Coordinates of viewRect
     GameObject viewRect; //The rect that will represent the viewable part of the game
     Plane xy; // The xy plane
     Mesh mesh;
     Vector3[] vertices  = new Vector3[4];
     int[] tri = { 0, 3, 1, 3, 2, 1 };
 
 
     void Start () 
     {
         mesh = new Mesh();
         mesh.vertices = vertices;
         mesh.triangles = tri;
 
         Vector3 pos = Camera.main.transform.position;
         pos.z = 0;
         viewRect = GameObject.CreatePrimitive(PrimitiveType.Quad);
         viewRect.transform.position = pos;
         viewRect.tag = "CameraView";
 
         viewRect.GetComponent<MeshFilter>().mesh = mesh;
     
         xy = new Plane(new Vector3(0,0,-1), Vector3.zero);
         CurrentView();    
     }
 
 
     void LateUpdate () 
     {
         CurrentView();
     }
         
     //Calculates what is visible by the camera 
     void CurrentView()
     {
         //Shoots rays out of each corner of the screen
         topLeft = Camera.main.ScreenPointToRay(new Vector3(0,Screen.height,0));
         topRight = Camera.main.ScreenPointToRay(new Vector3(Screen.width,Screen.height,0));
         botLeft = Camera.main.ScreenPointToRay(new Vector3(0,0,0));
         botRight = Camera.main.ScreenPointToRay(new Vector3(Screen.width,0,0));
 
         //Calculates topleft coordinate
         xy.Raycast(topLeft, out distance);
         tl = topLeft.GetPoint(distance);
 
         //Calculates topright coordinate
         xy.Raycast(topRight, out distance);
         tr = topRight.GetPoint(distance);
 
         //Calculates bottomleft coordinate
         xy.Raycast(botLeft, out distance);
         bl = botLeft.GetPoint(distance);
 
         //Calculates bottomright  coordinate
         xy.Raycast(botRight, out distance);
         br = botRight.GetPoint(distance);
 
         vertices[0] = bl; vertices[1] = br; vertices[2] = tr; vertices[3] = tl;
         tri[0] = 0; tri[1] = 2; tri[2] = 1; tri[3] = 0; tri[4] = 3; tri[5] = 2;
         mesh.vertices = vertices;
         mesh.triangles = tri;
         viewRect.GetComponent<MeshFilter>().mesh = mesh;
 
         GameObject test = GameObject.CreatePrimitive(PrimitiveType.Quad);
         test.transform.position = tr;
     
 
 
     
     }

Screenshot of what I was talking about with the test game object.