Postgresql Disk Allocation in Begin End Transaction

I have a loop in transaction block that creates a temporary table,updates,exports to txt file and drops table at the end of the block.
After some time I noticed that disk size was getting smaller each time loop continued.When I cancelled transaction block,disk size returned to its initial state.

How can I stop loop for allocating the disk on the following transaction ?

do
$$declare
  --variables
begin
     FOR r IN (SELECT ...) LOOP
        CREATE TEMPORARY TABLE TEST .. ;
        --UPDATE STATEMENTS
        --EXPORT (COPIES TABLE INTO TXT FILE)
        DROP TABLE TEST CASCADE;
     END LOOP;
end$$;