PLTDEV BTWN ACR X AND ACR Y.

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TAXIING FROM GATE AREA TXWY AND IN LINE OF ACFT TAXIING FOR DEPS FROM RWYS 12R/12L. PASSING TXWY C I RECEIVED A GND CALL WHICH I THOUGHT WAS 'CLRED RWY 6; ALPHA (?); FOLLOW MD80' THE MD80 IN FRONT OF ME WAS TURNING ONTO RWY 6 AND XING RWY 12R; THE ACTIVE RWY. AS I MADE THE TURN ONTO RWY 6 HDG NE I REALIZED I WAS HDG IN THE WRONG DIRECTION BUT I WAS TOO CLOSE TO THE ACTIVE TO STOP BECAUSE OF THE TFC ON FINAL APCH. I APPLIED PWR AND CROSSED RWY 12 R AS FAST AS POSSIBLE. AN MD80 ON FINAL MADE A GAR TO AVOID A POTENTIALLY DANGEROUS SIT. IN LATER CONVERSATION WITH THE TWR PERSONNEL; THEY SAID THE INSTRUCTIONS WERE TO TURN L ON RWY 6; ALPHA S AND FOLLOW ON MD 80 THAT WAS ALREADY ON ALPHA S TXWY. I DID NOT HEAR THE 'TURN L' INSTRUCTIONS AND COMBINED WITH THE VOLUME OF RADIO TFC AND MY UNFAMILIARITY WITH THE FIELD (MY FIRST TIME INTO STL) LED ME TO PUT THE ACFT INTO A POTENTIALLY DANGEROUS POS. THE ONLY RECOMMENDATION I WOULD HAVE FOR TAXI INSTRUCTIONS WOULD BE TO DROP THE REF TO 'RWY 6' AS I BELIEVE THAT'S WHAT LED ME TO TURN R WHEN I SHOULD HAVE TURNED L. I'LL ALSO BE A LOT MORE CAREFUL LISTENING TO TAXI INSTRUCTIONS.