Orthographic TopDown game Shooting Direction

Greeting,

I am having problem with calculation the right shooting direction in my orthographic topdown shooter. As I don't use true TopDown(I don't look on player right on top, but instead camera has about 45 degree angle) there is some distortions with correct shooting direction.

Take a look at screenshots(my win 8 doesn't include cursor in screenshots, so I painted it by hand)

when I look down or up, cursor, player direction and shooting direction ling up correctly, but when I look left or right distortion comes up:

because I use the code that rotates player to where mouse position is on the floor, player turns to that point, but gun is higher and the camera angle makes it appear that he is aiming at totally different direction.

Can you help me how to solve this problem, I want the player to always turn and aim at mouse position.

My code :

 void Update()
     {
         //Do raycast from the mouse position
         Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         
         RaycastHit hit;
 
         if (Physics.Raycast(ray, out hit, 100, floorMask))
         {
             //...and if it hit's something then update the look position
             //we do it this way in case the mouse didn't hit something, our character will have something to look at
             lookPos = hit.point;
         }
 
         //Find the direction we want to look at
         lookDir = lookPos - transform.position;

         //kill the y value
         lookDir.y = 0;
 
         transform.LookAt(transform.position + lookDir, Vector3.up);
         
     }