How can I eliminate the spaces and punctuation in a string with an assembly program in DOSBox?

I tried, but it gives me an error:

an unexpected end of file encountered

;Program p02.asm
.MODEL small
.stack 100h
.data

source  db  "STRING, WITH. PUNCTUATION : AND * SPACES!$"
aux     db  "                                          "
.code
  mov  ax, @data
  mov  ds, ax

;REMOVE EVERYTHING BUT UPPERCASE LETTERS.

  mov  si, offset source   ; POINT TO STRING.
  mov  di, offset aux      ; POINT TO AUXILIARY.
L1:
  mov  al, [ si ]          ; get character from source
;CHECK IF END STRING ($).
  cmp  al, '$'
  je   finale
;CHECK IF CHAR IS UPPERCASE LETTER.
  cmp  al, 65
  jb   is_not_a_letter    ; CHAR IS LOWER THAN 'A'.
  cmp  al, 90
  ja   is_not_a_letter    ; CHAR IS HIGHER THAN 'Z'.
;COPY LETTER TO AUX STRING.
  mov  [ di ], al
  inc  di                ; POSITION FOR NEXT CHARACTER.
is_not_a_letter:
  inc  si                ; move to next character
  jmp  L1

finale:
  mov  [ di ], al        ; '$', NECESSARY TO PRINT.

;PRINT STRING.  
  mov  dx, OFFSET aux
  mov  ah, 9
  int  21h

;END PROGRAM.
  mov  ax, 4c00h
  int  21h