C172 PLT CONFUSES INSTRUCTIONS AND TAXIES ONTO RWY FOR RUNUP.

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PRIOR TO STARTUP FOR DEP; I CONTACTED CLRNC DELIVERY FOR DEP INSTRUCTIONS AND A SQUAWK CODE; THEN CONTACTED GND. I WAS CLRED TO TAXI TO RWY 3 VIA TXWY B. GND INSTRUCTED ME TO FOLLOW THE TXWY OUT OF GA PARKING; AND TURN R AT TXWY B; WHICH I DID. I WAS UNABLE TO SEE A SEPARATE RUNUP AREA; SO UPON REACHING RWY 3; I STOPPED BEHIND THE RWY BOUNDARY; SWITCHED TO TWR FREQ; AND BEGAN MY RUNUP. TWR CALLED AND ASKED IF I WAS ON FREQ. I SAID I WAS; AND WAS TOLD THAT I WAS BLOCKING THE TXWY. I OFFERED TO INCH FORWARD AND TO THE SIDE SO THAT THE ACFT BEHIND ME COULD CROSS THE RWY; AND TWR TOLD ME THAT I SHOULD MOVE TO THE RUNUP AREA. I TURNED THE ACFT AROUND; POINTING IT NOW AT THE SIDE OF THE TXWY AWAY FROM THE RWY AND ASKED IF THE DIRECTION I WAS NOW POINTING WAS THE DIRECTION OF THE RUNUP AREA (IT WAS A WIDE TXWY; AND I THOUGHT THE FAR SIDE MIGHT BE THE RUNUP AREA). TWR TOLD ME 'NO; JUST GO TO THE END OF RWY 3.' I THOUGHT IT WAS AN UNUSUAL PLACE FOR A RUNUP; BUT I VISUALLY CONFIRMED THAT THERE WERE NO ACFT ON FINAL FOR RWY 3; AND THE TWR FREQ WAS CONGESTED; SO I SIMPLY RESPONDED 'END OF RWY 3.' AS SOON AS I WAS ON THE RWY; TWR CALLED AND ASKED IF I HAD ENTERED THE RWY -- EVIDENTLY SURPRISED THAT I HAD. I RESPONDED THAT I THOUGHT THAT'S WHAT HE HAD TOLD ME TO DO. HE RESPONDED THAT HE HADN'T; BUT NEVER MIND; I WAS CLRED TO POS AND HOLD RWY 3. MY PAX CONFIRMED THAT SHE HAD HEARD TWR TELL ME TO 'GO TO THE END OF RWY 3.' IN DISCUSSION AFTERWARDS; WE CONCLUDED THAT THE CTLR HAD MEANT THAT WE SHOULD HAVE GONE TO THE EXTREME SOUTHERN EDGE OF THE TXWY ADJACENT TO THE END OF RWY 3. THE SIT COULD HAVE BEEN AVOIDED IF: 1) I HAD ASKED GND ABOUT THE SPECIFIC LOCATION OF THE RUNUP AREA. 2) TWR HAD INDICATED 'THE TXWY ADJACENT TO THE END OF RWY 3' INSTEAD OF 'THE END OF RWY 3.' 3) I HAD CALLED FOR CONFIRMATION ON WHAT I THOUGHT WAS AN UNUSUAL INSTRUCTION.