C172 PLT FAILS TO CHANGE FROM APCH TO TWR FREQ; MISHEARS A CORRECTION FROM THE APCH CTLR AND CAUSES SEPARATION PROBS IN THE TFC PATTERN DUE TO LACK OF COM WITH TWR.

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I WAS FLYING ON AN IFR FLT PLAN FROM GCM TO FSM. CLOUDS WERE SCATTERED TO BROKEN AT 3000 FT. AFTER DSNDING ME TO 2200 FT; RAZORBACK APCH ASKED ME TO RPT THE FIELD IN SIGHT. AFTER CALLING THE FIELD; APCH CLRED ME FOR A VISUAL APCH TO RWY 25 AND INSTRUCTED ME TO CONTACT THE TWR. I ENTERED TWR FREQ INTO MY COMRDO AND PRESSED THE SWITCH FREQ BUTTON. I RPTED 'CESSNA XXXX WITH YOU VISUAL APCH RWY 25.' I THOUGHT I HEARD THE RESPONSE 'CONTINUE APCH.' FOR SOME REASON; I FAILED TO READ THE INSTRUCTION BACK. IF I HAD; I WOULD HAVE AVOIDED THE SITUATION AND REALIZED THAT WHAT WAS ACTUALLY SAID WAS 'ON APCH' MEANING I WAS STILL ON APCH FREQ. I ENTERED DOWNWIND; TURNED BASE AND AS I WAS TURNING FINAL BECAME CONCERNED THAT I HAD NOT BEEN CLRED TO LAND. I ASKED WHAT I THOUGHT WAS TWR IF I WAS CLRED TO LAND AND WAS THEN TOLD I SHOULD BE ON 118.3. I LEVELED OFF AND CHANGED FREQ TO HEAR THE END OF WHAT SOUNDED LIKE THE TWR CTLR SENDING ANOTHER ACFT AROUND. TWR GAVE ME LNDG CLRNC AND I LANDED WITH NO FURTHER PROBS. I COULD HAVE AVOIDED THIS SITUATION HAD I READ BACK WHAT I THOUGHT WAS 'CONTINUE APCH;' CHKED ON MY LNDG CLRNC SOONER. I'LL BE SURE TO READ BACK EVERYTHING IN THE FUTURE.