SCT CTLR DESCRIBES COM ERRORS WHICH COULD HAVE RESULTED IN A LOSS OF SEPARATION.

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THOUGH THERE WERE ONLY 4 ACFT ON MY FREQ AT THE TIME OF THE INCIDENT; THE SECTOR WAS BUSY AND I HAD JUST ASKED FOR A HDOF TO HELP ME OUT. I WAS BRIEFING MY HDOF TO LET THEM KNOW WHAT WAS GOING ON -- 2 TWRS WERE WAITING FOR US TO CALL THEM BACK FOR RELEASES ON IFR ACFT; WE NEEDED TO COORDINATE WITH 1 ADJACENT SECTOR FOR CTL OF AN ARR TO FUL (A C172) AND THEN MY HDOF COORDINATED WITH ANOTHER ADJACENT SECTOR TO PUT CRJ-9 ON THE LGB LOC TO GIVE ADDITIONAL SPACING BEHIND A PREVIOUS CESSNA LGB ARR. THOUGH THE FREQ DIDN'T SOUND BUSY; THE SECTOR WAS VERY BUSY. I HAD GIVEN THE C-172 A L TURN TO 070 DEGS TOWARD THE FUL FINAL APCH COURSE. SHORTLY THEREAFTER; CRJ CHKED ON AT 4000 FT FOR THE LGB LOC (RWY 30). I RESPONDED 'CRJ SOCAL APCH; ROGER. CESSNA 172; I'M SORRY; I'M GOING TO HAVE TO TURN YOU BACK TO THE RIGHT HDG 0-9-0.' I MISSED THE COMPLETE RESPONSE WHICH WAS 'OK 0-9-0 FOR NOW; CRJ.' WHEN I OBSERVED THE CRJ TURNING OPPOSITE DIRECTION TO THE FINAL; MY HDOF AND I IMMEDIATELY COORDINATED WITH THE ADJACENT SECTORS AND LUCKILY THERE WAS NO LOSS OF SEPARATION. WE ALSO WERE ABLE TO RESOLVE THE POTENTIAL CONFLICT OF THE C-172 AND THE TFC HE WAS TURNED TO AVOID. BOTH ACFT LANDED WITHOUT INCIDENT. HAD I NOT 'COMBINED' XMISSIONS; IT IS PROBABLE THAT THE CRJ WOULD NOT HAVE RESPONDED INCORRECTLY TO SOMEONE ELSE'S CTL INSTRUCTION. HAD THE CRJ USED HIS CALL SIGN IN THE RESPONSE INSTEAD OF JUST HIS NUMBERS; IT IS PROBABLE THAT I WOULD HAVE CAUGHT HIS MISTAKE.