CAPT OF A DHC8-200 MISTAKENLY TAXIED VIA AN INTERSECTING RWY INSTEAD OF XING IT DURING TAXI OUT FOR TKOF.

Narrative

RECEIVED CLRNC TO TAXI TO RWY 17R VIA TXWY M AND HOLD SHORT OF RWY 8/26. I READ BACK CLRNC AND CAPT ASKED ME TO REQUEST CLRNC TO DEPART FROM RWY 8. I ASKED AND RECEIVED CLRNC TO TAXI TO RWY 8; XING RWY 17R/35L AND HOLD SHORT OF RWY 8. LEAVING OUR GATE AREA; WE WERE TO TAXI VIA TXWY F; XING TXWY M AND THEN XING RWY 17R/35L; CONTINUING ON TXWY F AND THEN N ON TXWY C TO HOLD SHORT OF THE END OF RWY 8. I WAS RUNNING THE BEFORE TKOF CHKLIST; AND AS THE CAPT TURNED FROM TXWY F ONTO AND N ON RWY 17R/35L ENRTE TO RWY 8; I LOOKED UP AND SAID 'WE WERE CLRED TO CROSS THIS RWY; WHERE ARE YOU GOING?' I CALLED GND; AND THEY SAID TO CONTACT TWR FREQ FOR CLRNC FOR TKOF. THERE WAS NO OTHER TFC IN THE AREA AND WE DEPARTED NORMALLY. I SHOULD HAVE SUSPENDED RUNNING THE CHKLIST WHILE XING THE RWY 17R/35L AND BACKED UP THE CAPT. I DID HAVE THE ARPT DIAGRAM ON THE APCH PLATE HOLDER IN VIEW. CAPT SAID HE HAS ALWAYS BEEN CLRED THAT WAY AND GOT COMPLACENT. THIS WAS ONLY MY SECOND TIME TO LBB. I SHOULD HAVE BEEN EXTRA VIGILANT AT THE MOMENT OF XING THE RWY INSTEAD OF HAVING MY HEAD DOWN IN THE COCKPIT. ANOTHER LESSON LEARNED; SAFELY.