Hi Blue,
In the Class :
cl_salv_display_settings, It has the attribute FIT_COLUMN_TO_TABLE_SIZE
Data : lo_columns TYPE REF TO cl_salv_columns_table,
lo_columns = ob_salv->get_columns( ).
lo_columns->set_optimize('x').
lO_COLUMN->SET_OUTPUT_LENGTH('20').
"set the required width for each column.
Please check this links
http://scn.sap.com/docs/DOC-28429
http://scn.sap.com/thread/1190927
Hope this will help you to solve your problem.
Regards,
Vel