RWY INCURSION AND LWOC BY A LOW TIME STUDENT PLT IN A PA28 AT FLO; SC.

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I THINK THE MAIN CONTRIBUTING FACTOR WAS DISTR DUE TO AN UNFAMILIAR SIT. THIS WAS THE FIRST TIME I'D EVER ENTERED CLASS D AIRSPACE. PREVIOUSLY; I HAD SOLOED TWICE TO CLASS C AND I THINK I WAS EXPECTING TO BE UNDER POSITIVE CTL FROM THE MOMENT APCH ANSWERED MY INITIAL CALL-UP. INSTEAD; ON INITIAL CALL-UP; THE APCH CTLR SAID; 'CLRED VISUAL APCH; STRAIGHT-IN TO RWY 17.' SO; THE UNCERTAINTY OF NOT RECEIVING THE VECTORS/ALTS I WAS ERRONEOUSLY EXPECTING BECAME COUPLED WITH ANOTHER UNFAMILIARITY -- I HAD NEVER DONE A STRAIGHT-IN APCH. SOMEWHERE A FEW MI OUT; THE APCH CTLR CAME BACK AND SAID; 'CONTACT TWR 125.1' AND RIGHT AFTER THAT IS WHERE THE DISCONNECT HAPPENED. I HAD ALREADY DIALED THE TWR FREQ INTO STANDBY AS SOON AS I STARTED TALKING TO APCH; BECAUSE I KNEW THAT WAS WHOM I'D BE TALKING TO NEXT. I READ BACK THE FREQ TO THE APCH CTLR; BUT SOMETHING MUST HAVE DISTR ME AS I REACHED FOR THE SWITCH BECAUSE I NEVER SWITCHED OVER AND CALLED THE TWR. MAYBE BECAUSE THEY WEREN'T TELLING ME THE OTHER THINGS I HAD EXPECTED THEM TO; SOMEWHERE IN THE BACK OF MY MIND; 'VISUAL APCH; STRAIGHT-IN TO RWY 17' GOT TRANSLATED TO SOMETHING LIKE; 'CLRED TO LAND.' NEXT THING I KNOW; I'M PRETTY FAR DOWN FINAL; COPING WITH BEING HIGH; AND THE APCH CTLR CAME BACK AND REREAD HER PREVIOUS INSTRUCTIONS; 'CONTACT TWR 125.1.' I KNEW IMMEDIATELY I'D MESSED UP; BUT MY BRAIN WAS STILL OPERATING IN 'CLRED TO LAND' MODE. I READ IT BACK TO HER AND SWITCHED TO TWR AND CALLED 'FLORENCE TWR; WARRIOR XYZ.' BY THIS POINT I WAS ON SHORT FINAL. THE TWR CTLR DID NOT RESPOND TO MY CALL-UP. AFTER I LANDED AND CLRED THE HOLD SHORT LINE AND STOPPED; THEN THE TWR CTLR TOLD ME; 'XYZ; DID YOU SWITCH TO TWR WHEN INSTRUCTED?' 'NO SIR. I FAILED TO DO THAT. I'M SORRY.' 'CONTACT GND 121.0.' I WENT INSIDE AND CALLED THE TWR AND DISCUSSED WHAT HAD HAPPENED. I THINK THIS EVENT MIGHT NOT HAVE HAPPENED IF I HAD TAKEN MORE TIME TO LEARN THE OPERATIONAL DIFFERENCES BTWN CLASS C AND CLASS D.