A MOONEY M20E AFTER LNDG AND RECEIVING INSTRUCTIONS FROM THE TWR THE PLT BECAME DISORIENTED AND CONFUSED RESULTING IN A RWY INCURSION.

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UPON LNDG ON RWY 12R AT THE SAN ANTONIO INTL ARPT; I ADVISED THE LCL CTLR I WAS UNFAMILIAR WITH THE ARPT AND REQUESTED ASSISTANCE IN PROCEEDING TO THE FBO. THE TWR CTLR WAS VERY FRIENDLY AND HELPFUL AND INSTRUCTED ME TO STAY ON HIS FREQ AND TAXI VIA TXWY G TO TURN R ON TXWY N. I DID AS INSTRUCTED AND HELD SHORT OF TXWY A AS THE CTLR ALLOWED AN ACR TO TAXI ACROSS MY PATH. I WAS STILL ON TXWY G AT THIS TIME. THE CTRL GAVE ADDITIONAL ASSISTANCE AS I APCHED TXWY N. MY DEST ON THE FIELD WAS FBO AVIATION. I TURNED R ON TXWY N AS INSTRUCTED AND PROCEEDED SWBOUND TOWARDS MY ARPT DEST. IT WAS AT THIS POINT I BECAME DISORIENTED FOR WHATEVER REASON AND MISTAKENLY TURNED ONTO TXWY E. IN MY CONFUSION; I HONESTLY FEEL I FOLLOWED THE WRONG YELLOW TXWY CTRLINE MARKING. TXWY E PLACED ME ONTO RWY 03/21. I KNEW AT THIS TIME I HAD MADE A CRITICAL MISTAKE. THERE WERE NO ACFT USING RWY 3/21 AT THE TIME AND I QUICKLY EXITED THE RWY. I'M NOT SURE THE LCL CTLR EVEN NOTICED MY MISTAKE UNTIL I CALLED AND INFORMED HIM OF MY INCORRECT TURN. HE DIRECTED ME BACK ON COURSE AND NOTHING ELSE WAS SAID ON FREQ OF MY ERROR.