Narrative:

I believe this to be the case: according to tower (not having listened to the tapes), apparently I was cleared for left downwind entry runway 11. Anticipating another clearance, I entered right downwind 36. Shortly after reporting and joining right downwind for runway 36, tower pointed out some traffic. At that time traffic past 20-30' beneath me. #2 was cleared for right turn after takeoff. I was flying #1.

Google
 

Original NASA ASRS Text

Title: PLT OF SMA ENTERED TRAFFIC PATTERN CONTRARY TO TWR INSTRUCTIONS. HAD NMAC WITH ACFT TAKING OFF.

Narrative: I BELIEVE THIS TO BE THE CASE: ACCORDING TO TWR (NOT HAVING LISTENED TO THE TAPES), APPARENTLY I WAS CLRED FOR LEFT DOWNWIND ENTRY RWY 11. ANTICIPATING ANOTHER CLRNC, I ENTERED RIGHT DOWNWIND 36. SHORTLY AFTER RPTING AND JOINING RIGHT DOWNWIND FOR RWY 36, TWR POINTED OUT SOME TFC. AT THAT TIME TFC PAST 20-30' BENEATH ME. #2 WAS CLRED FOR RIGHT TURN AFTER TKOF. I WAS FLYING #1.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.