AN SMA HAD TO ABORT ITS 'LOW PASS' DUE TO AN ACFT ON THE RWY.

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AT DEP; I REQUESTED A HIGH SPD LOW PASS AS I HAVE DONE MANY TIMES IN THE PAST. ON DOWNWIND; TWR CLRED ME FOR A LOW APCH BEHIND A TWIN THAT WAS LNDG. CTLR SPECIFICALLY REQUESTED I DO THE LOW APCH OVER THE RWY. AS I WAS ON THE LOW APCH; AT ABOUT 160 MPH AND ABOUT 100 FT AGL; I SAW I WAS COMING CLOSER THAN I HAD EXPECTED TO THE TWIN THAT WAS STILL ON THE RWY STARTING TO TURN OFF. CTLR SAID 'TURN R.' I TURNED R IMMEDIATELY; 45 DEGS; AND STARTED TO CLB AND DEPARTED THE PATTERN AS PREVIOUSLY CLRED. I HAVE CONTINGENCIES IN MY MIND WHEN I DO LOW APCHS: I HAVE THE MOMENTUM TO PULL UP AND DEPART OR EVEN LAND ON THE REMAINING RWY; ALSO I CAN TURN TO ONE SIDE OR ANOTHER AND ALSO THROTTLE BACK. LATER I REALIZED THAT; ALTHOUGH I FELT SAFE IN THIS LOW APCH AND HAD THOUGHT THROUGH MY CONTINGENCIES; I PERHAPS CAME CLOSER TO THE ACFT ON THE RWY THAN WAS PRUDENT. I HAD GAINED TOO RAPIDLY ON THE LNDG TWIN. I'M NOT SURE OF MY ALT; AS I WAS LOOKING OUTSIDE. I WAS ON THE R SIDE OF THE RWY AND THE TWIN ON THE L SIDE (RWY IS 150 FT WIDE). IN THE FUTURE; WHEN I'M CLRED FOR A LOW APCH; I WILL PLAN MY PATTERN BETTER; ESPECIALLY IF I'M FOLLOWING ANOTHER ACFT; I WILL HOLD MY ALT HIGHER; IF SOMEONE IS STILL ON THE RWY I WILL PULL UP SOONER AND KEEP A WIDE CLRNC.