Do you mean that all 20 columns fit on one page in the LISTING window, but not in RTF output???
That's because LISTING and RTF are governed by different assumptions... For example LISTING uses SAS linesize and pagesize options and RTF dest does not. LISTING uses HEADLINE and HEADSKIP options and RTF does not, etc, etc.
For some ideas on how to fit "very wide" output in RTF and PDF destinations, search for a previous forum posting on "dealing with very wide tables" -- there are some code samples there.