SMT PLT RETRACTS GEAR INSTEAD OF FLAPS ON LNDG ROLLOUT.

Narrative

ON THE DAY IN QUESTION; I WAS CALLED TO COVER ANOTHER PLT'S RTE. MY NORMAL RTE WAS FLOWN WITH AN SMA. I HAD ONLY 15.9 HRS IN THE SMT AT THE TIME AND MY TRAINING ONLY CONSISTED OF 2 FLTS. I TOOK OFF OUT OF SIOUX FALLS; SD; AND STARTED ON MY WAY TO MARSHALL; MN; MML. TWR RADIOED ME; AND INFORMED ME THAT COMPANY WANTED ME TO COME BACK AND LAND TO PICK UP A BAG OF FREIGHT THAT WAS MISSED. SO I ENTERED A L DOWNWIND FOR RWY 15 FSD. DUE TO ANOTHER ACFT APCHING THE RWY FROM BEHIND ME AND RUNNING LATE; I WAS IN A BIG HURRY TO MAKE IT BACK TO THE RAMP. ON LNDG ROLLOUT; I NEED TO MAKE A TXWY TURNOFF; SO TO INCREASE MY BRAKE EFFECTIVENESS I WENT TO PULL UP THE FLAPS BUT INADVERTENTLY PULLED THE GEAR SWITCH TO THE UP POS FOR A SPLIT SECOND. DUE TO THIS; THE L LNDG GEAR DISENGAGED; AND COLLAPSED. THE ACFT SLID OFF THE L SIDE OF THE RWY INTO THE INFIELD. THERE WAS DAMAGE TO THE L LNDG GEAR; L PROP AND L WING. THE REASON I PULLED THE LNDG GEAR UP WAS A COMBINATION OF FACTORS: 1) THE FLAP SWITCH ON SMA IS LOCATED IN THE SAME SPOT AS THE GEAR SWITCH ON THE SMT. 2) STRESSFUL SIT; BECAUSE OF THE FREIGHT BEING LEFT BEHIND AND BEING IN A HURRY. 3) INSUFFICIENT TRAINING IN ACFT. 4) LOW FLT TIME IN ACFT.