NMAC IN THE TFC PATTERN BTWN A LOW TIME C182 PVT PLT AND A BONANZA ON THE DOWNWIND LEG FOR RWY 32R AT CCR; CA.

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WHILE APCHING AN UNFAMILIAR ARPT; CONCORD BUCHANAN; THERE WAS QUITE A BIT OF TFC. ON CONTACTING THE TWR; SHE CLRED ME DOWNWIND ON RWY 32R. I STATED THAT I WANTED TO GO TO THE VOR WHICH PLACES ME ON A 45 DEG ENTRY FOR THIS RWY. SHE DID THAT. UPON REACHING THE VOR; I CALLED IN AND WAS TOLD TO ENTER THE 45 DEG FOR RWY 32R. THERE WAS A BONANZA APCHING FROM THE NE AS WELL. I THOUGHT HE WAS SOME DISTANCE FROM ME AS I ASSUME THE CTLR DID. HE WAS TOLD TO COME IN ON THE 45 DEG AS WELL. JUST AS I WAS GETTING READY TO TURN DOWNWIND; THE BONANZA OVERTOOK ME OFF MY L WING AT APPROX 300-500 FT AWAY. I BELIEVE THAT THE CTLR NOTICED THIS AND TO SAVE TIME; SHE TOLD ME TO CROSS OVER TO THE OTHER SIDE AND THEN CLRED ME TO LAND RWY 32L. MY ERROR WAS THAT I THOUGHT TWR CLRED ME FOR THE SAME RWY 32R; BUT; IN FACT; HAD BEEN CLRED FOR RWY 32L; A MUCH SMALLER RWY WHICH IS STAGGERED SIGNIFICANTLY FROM RWY 32R. IN RETROSPECT; WHAT I ASSUMED TO BE HER CLRNC MADE NO SENSE; AND SHOULD HAVE TRIGGERED MY INNER VOICE WITH MANY QUESTIONS. I ALSO HAD SOME DEG OF TUNNEL VISION AS MY ORIGINAL PLAN WAS FOR RWY 32R AND I HADN'T MENTALLY PREPARED FOR THE OTHER RWYS. I ALMOST ASKED FOR A 360 DEG TURN TO THE R TO INCREASE SEPARATION; BUT WAS WORRIED THAT THERE WAS TFC BEHIND ME AS WELL. IN RETROSPECT; I SHOULD HAVE DONE THIS OR ASKED TO GO OUTBOUND ON THE RWY TO GET RE-ESTABLISHED IN THE TFC PATTERN THAT I HAD PREPARED FOR. I WAS EXTREMELY FLUSTERED BY THIS CLOSE TFC AND FELL BEHIND ON MY SITUATIONAL AWARENESS AND MY JUDGEMENT. THE OTHER CONTRIBUTING FACTOR IS THE FACT THAT RWY 32L WAS SO FAR INBOUND COMPARED TO RWY 32R; THAT IT WAS BEHIND ME WHEN I ACTUALLY TURNED DOWNWIND. NEXT TIME I WILL BE PREPARED FOR OTHER CONTINGENCIES AND WILL PREPARE TO GET OUT OF THE AREA; REGROUP AND TRY AGAIN AND GO AROUND. THE SCARIEST PART OF THIS IS THAT I WAS CONFUSED; BUT DID NOT REALIZE IT. I SHOULD ALSO HAVE BEEN MUCH CLEARER THAT I WAS UNFAMILIAR WITH THE ARPT.