GA SMA RWY TRANSGRESSION AFTER LNDG AT FMY.

Narrative

I WAS 'CLRED TO LAND ON RWY 5' WITH INSTRUCTIONS TO 'HOLD SHORT OF RWY 15.' I LANDED AND HELD SHORT OF RWY 15 BY COMING TO A COMPLETE STOP APPROX 1 AIRPLANE LENGTH FROM RWY 15. THE TWR THEN SAID; 'MAKE A 180 DEG ON THE RWY AND TAXI BACK; ETC.' I INITIATED A 180 DEG TO THE L AND IN DOING SO WENT ONTO RWY 15 APPROX 1 WINGSPAN OF MY SMA ACFT. THIS WAS THE TIGHTEST TURN MY ACFT COULD MAKE. WHEN I WAS APPROX HALFWAY THROUGH THIS 180 DEG TAXI TURN; THE TWR TOLD AN ACFT ON SHORT FINAL FOR RWY 15 TO 'GAR.' I OBSERVED THIS ACFT AFTER THE TWR TOLD HIM TO GAR AND I OBSERVED THAT A GAR BY HIM WAS NOT NECESSARY AS HE WAS NOT YET OVER THE NUMBERS AND I HAD COMPLETED MY 180 DEG TURN AND WAS EXITING THE RWY. AT THE SAME TIME I XMITTED THAT 'I WOULD BE CLR OF THE INTXN IN APPROX 2 SECONDS.' THE OTHER ACFT CONTINUED HIS GAR ANYWAY. SOLUTION: THE TWR SHOULD HAVE SAID TO ME; 'CAN YOU MAKE A 180 DEG FROM YOUR POS WITHOUT TAXIING UPON RWY 15?' ALSO; JUST PRIOR TO THE TWR INSTRUCTING ME TO 'MAKE MY 180 DEG'; AN ACFT THAT JUST LANDED ON RWY 15 ROLLED THROUGH THE INTXN PAST ME AND TURNED OFF TO HIS R ON THE RWY 5 PARALLEL TAXIWAY. I THOUGHT THAT THIS LNDG ACFT WAS THE REASON THE TWR HAD ME HOLD SHORT OF RWY 15.