Write to file in Assembly Lanugage

.model small
.stack
.data
buffer db "I'm writing.",'$'
file db "myfile.txt",0


.code
mov ax,@data
mov ds,ax
 
mov dx, offset file
;mov al,0            ;Open file (read-Only)
mov al,1            ; Write only
;mov al,2            ; Read & Write
mov ah,3dh           ; Load File handler and store in ax
int 21h

mov cx,10            ; no. of bytes to be written. I want only first 10 bytes to be written in my already created file
mov bx,ax            ; Move file Handler to bx
mov dx,offset buffer ; load offset of string which is to be written to file
mov ah,40h
int 21h

mov ah,4ch
int 21h
end