AN EARLY TURN TO BASE LEG AT SNA; CA; PRODUCES A TFC CONFLICT WITH AN ACFT ESTABLISHED ON FINAL APCH.

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ON APCH TO SNA FROM THE NW; I WAS HANDED OFF FROM SOCAL APCH TO SNA TWR. AFTER CHKING IN WITH TWR; I WAS INSTRUCTED TO ENTER A R DOWNWIND FOR RWY 19R; WHICH I DID. ABOUT 1 MIN LATER; TWR SAID THAT 'ACFT X IS FOLLOWING A TWIN CESSNA ON 2 MI FINAL; CLRED TO LAND RWY 19R #2 AFTER THE TWIN.' I MISTOOK THIS XMISSION TO MEAN THAT THE TWIN WAS PAST ME; AND THAT I SHOULD TURN BASE. AFTER I STARTED A TURN TO BASE; TWR CALLED AND SAID THAT I WAS SUPPOSED TO BE ON A DOWNWIND; AND THAT I SHOULD TURN L. AS I WAS TURNING BACK TO THE DOWNWIND COURSE (010 DEGS). I HAD VISUAL CONTACT WITH THE TWIN CESSNA ON FINAL FOR RWY 19R; WHICH WAS ABOUT 700 FT BELOW ME. THE TWIN PLT INDICATED THAT HE ALSO HAD ME IN SIGHT. I WAS RESEQUENCED AND LANDED UNEVENTFULLY. I HAD THOUGHT THAT THE TWR WAS INDICATING THAT THE ACFT ON FINAL WAS NOT A FACTOR. WHAT I SHOULD HAVE DONE IS EITHER VISUALLY VERIFY THAT THE ACFT WAS PAST ME; OR ASK THE TWR TO CONFIRM THAT THE ACFT WAS PAST ME; AND NO FACTOR. I HAVE DISCUSSED THE PRACTICES AT SNA WITH A LCL INSTRUCTOR; AND BELIEVE THAT I HAVE A BETTER UNDERSTANDING OF PATTERN OPS.