Why is mouse position incorrect?

Question

I use Windows 8.1 and an emulator for assembly 8086.

I want to design a program in assembly that draws 4 squares and when user clicks on each of them paints this. For example I draw square in position (50,50) to (100,100) pixel, but when click on square, mouse position incorrect, for example 150, while end of square on 100 Pixel.

macro mosPos 

  local L  

   mov ax, 1
   int 33h

 L:mov ax, 3
   int 33h
   cmp bx, 1
   jne L

   mov XMouse, cx
   mov YMouse, dx

endm