ACFT ON IPC FLT ENTERED RWY AT SNA.

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IFR TRAINING FLT. PREPPING FOR IPC. HAD FLOWN ILS RWY 19R AT SNA; LANDED; TAXIED CLR ON TXWY H; WAS IN TWR RUN-UP AREA. COPIED IFR CLRNC; AND RECEIVED TAXI CLRNC TO RWY 19R VIA TXWY B. TWR THEN CHANGED TAXI CLRNC TXWY B TO TXWY J; HOLDING SHORT RWY 19R. I COMPLIED. NEXT; CLRED TO CROSS ACTIVE RWY 19R. INACTIVE RWY 19L; L ON TXWY C; TO KILO; HOLD SHORT RWY 19L AT KILO. I CROSSED RWY 19R; AND AS I STARTED ACROSS RWY 19L; THERE WERE 2 B737'S ON TXWY AWAITING TAXI. BECAUSE I WAS IN A SMALL CESSNA 152 STARING AT 2 B737'S AHEAD OF ME; I TURNED ONTO RWY 19L; THINKING IT WAS TXWY C. I DID NOT WANT TO GET TOO CLOSE TO THE B737'S. AFTER I HAD TURNED INTO RWY 19L; AND AFTER GOING ABOUT 50 FT; I REALIZED MY MISTAKE. I IMMEDIATELY TURNED AROUND AND WAS HEADING FOR TXWY J. AT THIS POINT; THE CTLR SAID WHAT I HAD DONE; AND SAID 'THAT'S OK;' OR WORDS TO THAT EFFECT. THERE WERE NO OTHER ACFT ON THE RWY; WHICH APPEARED INACTIVE. THE CTLR TOLD ME TO CONTINUE AS PREVIOUSLY INSTRUCTED; AND IT WAS NOT A PROB. IT WAS AT LEAST MOMENTARILY CONFUSING; DUE TO THE WX; SLICK PAVEMENT; TRYING TO FOLLOW A RATHER 'CIRCUITOUS' TAXI RTE; WHICH ATC DID APOLOGIZE FOR. WE EVEN HAD A TAXI DIAGRAM OUT; BUT THE B737'S LOOKED RATHER IMPOSING/INTIMIDATING. NEXT TIME; I WILL TAKE IT A BIT SLOWER AND CHK BEFORE TURNING AT SNA. TXWY K IS RELATIVELY CLOSE TO TXWY C; AND I DO NOT GO THERE REGULARLY. IT COULD HAPPEN TO ANYONE. LESSON LEARNED!