SQL & PL/SQL

Hi

I have a script (see below) which runs and spools the information

select
STU_ID||','||CRSLIST||','||FIRST_NAME||','||SURNAME||','||MID_INITIAL||','||substr(rtrim(STU_ID),-1)||','||STUREF studata
from LOC_STUEMAIL
where STU_ACT = 'A'
order by STU_ID

I spool it to csv file. The STUREF is a number field.
The script does what it is suppose to do. The issue is there are lots of space in the spool file after STUREF field which I want to eliminate. I have tried RTRIM but it is not eliminating them.

Any help please