BARON 58 PLT INADVERTENTLY RETRACTS LNDG GEAR DURING LNDG ROLL.

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UPON ENTRY TO L DOWNWIND RWY 28; I WENT THROUGH AND COMPLETED THE BEFORE LNDG CHKLIST; VERIFIED '3 GREENS' DOWNWIND; BASE AND FINAL. ON BASE; PROPS WENT FORWARD AIRSPD AT BLUE LINE; ON FINAL ADDED REMAINING FLAPS. ON SHORT FINAL; OBSERVED XWIND AT AN ESTIMATED 5-10 KTS AT SOCK. NOTICED A ROAD AND TFC VERY CLOSE TO RWY THRESHOLD. FLEW RIGHT OVER A CAR AT ABOUT 20 FT. SPD AT 100 KTS; FLOATED DOWN RWY IN FLARE; TOUCHED DOWN ABOUT 500 FT DOWN THE RWY. THE AIRPLANE I PWRED TO IDLE. I DIDN'T WANT TO RUN OFF THE END. FOR MAX BRAKE EFFECTIVENESS; I THOUGHT TO RAISE THE FLAPS. A WIND GUST DIRECTED MY ATTN TO THE ROLLOUT PATH AND STAYING ON THE RWY; I REACHED OUT TO RAISE THE FLAPS WITH MY ATTN STILL OUTSIDE THE ACFT. THE HORN SOUNDED AND I IMMEDIATELY KNEW WHAT I HAD DONE. I IMMEDIATELY REVERSED THE ACTION. HOWEVER; THERE WAS INSUFFICIENT WT FOR A MOMENT DURING THE GUST ON THE MAINS TO ACTIVATE THE SQUAT SWITCH ON THE GEAR AND IT BEGAN TO TRANSITION. AS IT DID; THE R WING CONTACTED THE GND; THEN THE NOSE; AND THEN THE L WING CAME DOWN AS THE GEAR RETRACTED. I SKIDDED DOWN THE RWY AND OFF INTO THE GRASS; TAKING OUT 1 RWY LIGHT. CONTRIBUTING FACTORS: THIS WAS THE SHORTEST AND NARROWEST RWY I'D LANDED ON IN THIS AIRPLANE -- 50 FT BY 3500 FT. I KNEW THIS AND WANTED TO BE SURE I COULD STOP BY THE END. ANOTHER CONTRIBUTING FACTOR IS THAT I HAVE CONSIDERABLY MORE TIME IN B55 BARONS AND 136 BONANZAS THAN I DID IN THE P58 BARON. THE FLAP AND GEAR POS LEVERS ARE IN SIMILAR PLACES ON THE PANEL ONLY THEY ARE BACKWARDS IN THE P58. I INSTINCTIVELY REACHED FOR THE LEVER I WAS USED TO REACHING FOR IN THE OTHER ACFT. WHILE THESE ARE VIABLE CONTRIBUTING FACTORS; NOTHING CAN EXCUSE THE FACT THAT I FAILED TO PROPERLY IDENT THE COMPONENT BEFORE ACTIVATING IT. I USUALLY DO; BUT THIS TIME DIDN'T. IT IS A LESSON LEARNED THE MOST UNFORTUNATE WAY.