SMA LANDS WRONG RWY; USES PARALLEL.

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WAS ON INST FLT FROM BEND; OR; TO PDX ARPT. BROKE OUT OF CLOUDS AT APPROX 5000 FT AND WAS GIVEN A VISUAL TO RWY 10R. WAS ASKED TO MAKE A R DOWNWIND TO RWY 10R. WHILE STILL AT APPROX 3500 FT WAS ASKED TO CROSS OVER THE FIELD AND MAKE A L DOWNWIND TO RWY 10L. BECAUSE OF THE CONFUSION ON SHIFTING RWYS I CROSSED OVER THE FIELD; MADE A L DOWNWIND WHILE ATTEMPTING TO LOSE NEARLY 3000 FT OF ALT. WHILE TURNING L BASE FOR RWY 10L I OBSERVED A SMALL COMMUTER AIRLINE MAKING AN APCH FOR RWY 10R AND JUST FOLLOWED HIM IN TO RWY 10R. I THOUGHT THE CTLR HAD ASKED ME TO FOLLOW HIM IN. AS I LINED UP ON FINAL ABOUT 1 MI OUT; I ASKED THE CTLR IF I WAS TO LAND ON RWY 10R BECAUSE I WAS UNCLR AT THAT MOMENT. SHE SAID 'NEGATIVE' AND ASKED THE AIRPLANE BEHIND ME TO GAR. I STILL HAD SPACE TO SHIFT TO RWY 10L OR GAR BUT FELT HER RESPONSE MEANT I SHOULD CONTINUE LNDG ON RWY 10R. NO OTHER INCIDENT OR CLOSE CALL AROSE AND I TAXIED TO THE ARPT TERMINAL PER THE GND CTLR'S INSTRUCTIONS. I BELIEVE I WAS NOT AS ATTENTIVE AS NECESSARY AND IN THE ABSENCE OF ANY OTHER INSTRUCTIONS OR COM WHILE LNDG; THE CTLR WAS NOT ATTENTIVE. BECAUSE OF MY HIGH ALT OVER THE ARPT I HAD NOT BEEN CLRED TO A LOWER ALT UNTIL I WAS GIVEN A 'VISUAL' TO LAND ON RWY 10R. EVEN AS MY INSTRUCTIONS WERE CHANGED TO RWY 10L I HAD TO RAPIDLY LOSE ALT ON MY DOWNWIND AND BASE LEG AND IT WAS JUST A NATURAL TO DSND DOWN TO RWY 10R. IT ALSO APPEARED THE CTLR WAS TRYING TO COMPENSATE FOR MY LOCATION OVER THE ARPT AFTER MY RELEASE FROM APCH CTL AND MAY HAVE MISJUDGED MY ALT. WE WERE BOTH IN ERROR IN MY OPINION.