SIMILAR CALL SIGNS CONTRIBUTE TO A RWY INCURSION AND A GO AROUND.

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I WAS INVOLVED IN GETTING CHKED OUT IN A P28R/200 AT WHP. THIS WAS MY SECOND TIME OUT WITH THE SAME INSTRUCTOR AS THE FIRST TIME WE HAD INSUFFICIENT LIGHT TO COMPLETE THE CHK-OUT. WE HAD STARTED AROUND XA00 PM AND COMPLETED 6 LNDGS AT WHP. DURING THESE LNDGS WE WERE FOCUSED ON AIRSPDS AND CONFIRMING '3 GREEN' DURING EACH SEGMENT OF THE PATTERN. I WAS AWARE OF A HELI PRACTICING IN THE PATTERN AS WELL WITH A SIMILAR SOUNDING CALL SIGN TO MINE. MINE WAS XXX AND THE HELI'S SOUNDS LIKE XXY. AFTER MY 6TH LNDG; I TAXIED BACK TO RWY 30 AND CALLED TWR TO SAY I WAS READY FOR TKOF. I WAS TOLD TO 'HOLD SHORT.' THE HELI ALSO CALLED 'READY FOR CLOSE PATTERN.' I HAD CALLED 'READY FOR STRAIGHT OUT DEP.' BOTH THE HELI AND I WAITED; HE AT AN INTXN; AND I AT THE END OF RWY 30. TWR WAS TALKING TO OTHER TFC DURING THIS TIME. INSIDE THE PLANE THE INSTRUCTOR AND I WERE DISCUSSING CRITERIA HE WANTED TO SEE IN ORDER TO FEEL ABLE TO CHK ME OUT. AFTER A FEW MINS TWR CALLED THE HELI 'WITHOUT DELAY; CLRED FOR IMMEDIATE TKOF R CLOSED PATTERN APPROVED.' I HEARD THE HELI'S CALL SIGN AS MINE AND SO DID THE INSTRUCTOR AND I ANSWERED 'XXX CLRED FOR IMMEDIATE TKOF.' AS I CROSSED THE HOLD SHORT LINE I ADDED; APPROX 10 SECONDS LATER; 'AND XXX WILL BE A STRAIGHT OUT DEP.' TWR PROMPTLY RESPONDED THAT THE CLRNC WAS NOT FOR ME; BUT THE HELI. I STOPPED APPROX 15 FT FROM THE HOLD SHORT LINE BEFORE TURNING TO BE STRAIGHT WITH THE RWY. TWR HAD LNDG TFC THAT HE HAD CLRED TO LAND DO A GAR AND THEN CLRED ME TO TAKE OFF. I SEE SEVERAL FACTORS WHICH CONTRIBUTED TO MY MISTAKE: 1) I WAS TENSE ABOUT THE CHK OUT AND NOT FULLY CONCENTRATING ON MY SITUATIONAL AWARENESS; 2) I WAS EMOTIONALLY ASSUMING THAT THE INSTRUCTOR WOULD BE CORRECT IN WHAT WAS SAID SINCE HE HAD MORE TRAINING THAN ME; 3) TWR SAID NOTHING WHEN I FIRST RESPONDED AND ONLY TOLD ME OF MY MISTAKE AFTER I ADDED THE PART ABOUT THE 'STRAIGHT OUT DEP.' WHILE I FULLY ACCEPT MY RESPONSIBILITY AND MISTAKE I FEEL THAT NOT HEARING ANYTHING AFTER I CALLED BACK MY CLRNC LED ME TO BELIEVE I HAD HEARD ACCURATELY WHEN I HAD NOT. THIS SIT COULD HAVE BEEN AVOIDED IN THE FOLLOWING WAYS: 1) PRIORITIZING SITUATIONAL AWARENESS DURING CRITICAL TIMES DURING TKOF IS A MUST FOR ME; 2) I MUST HAVE MORE CONFIDENCE IN MY ABILITY TO QUESTION CTL DIRECTLY AND NOT RELY ON OTHER'S WITH ME WHO HAVE MORE EXPERIENCE; AND 3) I MUST NOT REACT; BUT RATHER RESPOND BY REMAINING CALM WHEN I HEAR TWR SAY 'WITHOUT DELAY' PLUS A DIRECTION. I HAVE LEARNED THAT LISTENING INCLUDES REDUCING EMOTIONAL INTERFERENCE AND IS A MAJOR RESPONSIBILITY PLACED UPON ME AS PIC.