How do you control the length of the column heading?

Hello,

I'm creating an ad-hoc report.  I having problems getting a column heading to be the same size as the reported date.  In the same code and output below, I want the column, "programz", to be the same length as the field name, 'program', which I've truncated (to 42 characters) using the 'substr' function.  I'm using the column command thinking this will control the length of the column heading.  As you can see the output is not behaving as I would want.  What am I doing wrong?  Thank you.

SQL> set linesize 100
set pagesize 40
ttitle 'Sample report title'
column programx format a42