19c Database and getting ORA-01422: exact fetch returns more than requested number of rows

DECLARE

 v_blob BLOB;

 v_len NUMBER;

 v_file_name VARCHAR2(100);

 v_output utl_file.file_type;

 v_totalsize NUMBER;

 v_position NUMBER := 1;

 v_chucklen NUMBER := 4096;

 v_chuck RAW(4096);

 v_remain NUMBER;

 v_atfilecontentno char(18);

cursor c_files is

   SELECT dbms_lob.Getlength (atc.filecontent), atc.atfilecontentno, atc.atfilecontentno || '.' || ext.extension || '.gzip'

   from atfilecontent atc, atfileproperties afp, atmimetype mt, FILEEXTTOMIMEMAPPING ext

   where atc.atfilecontentno = afp.atfilecontentno

   and afp.atmimetypeno = mt.atmimetypeno

   and mt.code = ext.mimetype

   and atc.atfilecontentno > 0;

BEGIN

   OPEN c_files;

   LOOP

       FETCH c_files INTO v_totalsize, v_atfilecontentno, v_file_name;

       EXIT WHEN c_files%NOTFOUND;