A* pathfinding with Tilemap

hi there
i want to create A* pathfinding using this tutorials from sebastian lague using a unity 2d tilemap:

the problem is when i move the seeker position.y up to -2, the node path seems to go down about 2 nodes.

i've been modifying the NodeFromWorldPoint() method a little bit so the x coordinates seems to be good, but still have this problem from the y coordinates. here is the method code:

Code (CSharp):

1. public Node NodeFromWorldPoint(Vector3 worldPosition)
2.     {
3.         float percentX = (worldPosition.x + gridSizeX / 2) / gridSizeX;
4.         float percentY = (worldPosition.y + gridSizeY / 2) / gridSizeY;
5.         percentX = Mathf.Clamp01(percentX);
6.         percentY = Mathf.Clamp01(percentY);
7.  
8.         int x = Mathf.RoundToInt((tileMap.size.x - 1) * percentX);
9.         int y = Mathf.RoundToInt((tileMap.size.y) * percentY);
10.         return grid[x-1, y];
11.     }

this is my first thread post, so i'm sorry for my bad english ^-^