AN ATX FLC ATTEMPTED TO TKOF ON THE WRONG RWY AT HOU.

Narrative

WE WERE CLRED FOR TKOF AFTER TAXIING DOWN THE PARALLEL TXWY FOR RWY 4 AT HOU. I ROLLED ONTO THE RWY AT THE JUNCTION OF RWY 4 AND RWY 36 AND LINED UP ON RWY 36 BY MISTAKE. I AND THE TWR CAUGHT MY MISTAKE AT ABOUT THE SAME TIME AT ABOUT 50 KTS. WE STOPPED; BACK TAXIED TO RWY 4; AND WERE CLRED FOR TKOF RWY 4. AS WE WERE TAXIING DOWN THE PARALLEL; TWR CLRED US FOR TKOF AND TURN L TO 020 DEGS; WHICH I SET WITH THE HDG BUG; BUT FOR THE FIRST TIME I NEGLECTED TO CHK THE CDI THAT WAS SET TO 040 DEGS. I THINK THE LAID BACK ATTITUDE DUE TO EARLY MORNING GO AFTER LONG PREVIOUS DAY AND TWR INSTRUCTION TO TURN L TO 020 DEGS MAY HAVE CONTRIBUTED TO MISTAKE; I AM NOT SURE! BUT I AM SURE OF HOW I CAUGHT THIS MISTAKE AND HOW TO PREVENT IT AGAIN. AS WE ACCELERATED I NOTICED THE BLACK 1000 FT MARKER AS WE APCHED IT (RWY 4) AND I KNEW THAT I SHOULD HAVE MORE THAN 7000 FT ON RWY 4. SO I STOPPED; THEN CHKED THE CDI. IF I HAD CHKED THE CDI FIRST I WOULD NOT BE WRITING THIS ASRS RPT. ALSO; THE TWR WAS VERY FORGIVING -- BOTH ON ME AND ON MY EGO!