LOW TIME GA PLT CONFUSES ISP FOR FRG AND INADVERTENTLY ENTERS ISP'S CLASS C AIRSPACE.

Narrative

I TAXIED FROM THE RAMP TO THE RUNUP AREA AND AT THAT POINT REALIZED HOW MUCH TFC WAS AT FRG. I HELD FOR TKOF FOR 30 MINS WHILE THE TWR; OPERATING ON 2 FREQS; TRIED TO CTL TFC BY HAVING THEM HOLD RIGHT OUTSIDE THE PATTERN. THERE WERE UP TO 8 PEOPLE LET INTO THE PATTERN AT ONE TIME -- BOTH DOWNWIND AND STRAIGHT-IN ENTRIES. AFTER BEING DENIED TOUCH-AND-GOES; I DEPARTED TO THE N. AFTER 40 MINS OF MANEUVERS; I ATTEMPTED RETURN TO THE ARPT (CLASS D). THEY WERE USING 2 FREQS FOR TWR. I WAS TOLD STAND BY 5 MINS TWICE AND THEN RECEIVED INSTRUCTIONS TO PROCEED TO DEER PARK. THERE WERE 4-5 ACFT HOLDING OVER THE DEER PARK VOR. THERE IS A 1 1/2 MI CORRIDOR BTWN REPUBLIC'S CLASS D AND ISLIP'S CLASS C (15 NM CTR-TO- CTR). WHAT I BELIEVED TO BE REPUBLIC WAS IN FACT ISLIP AND IT WAS DISCOVERED WHEN I REALIZED RWY ALIGNMENT AND KEYED OFF BY REPUBLIC TWR NOT ABLE TO LOCATE ME ON RADAR. I THEN CALLED APCH; NOTIFIED THEM OF MY POS AND ALT; AND RECEIVED A VECTOR BACK TO REPUBLIC ARPT. I WAS DISORIENTED AS TO MY POS. IT WAS GETTING CLOSE TO DUSK AND THERE WAS A GREAT DEAL OF GLARE. I WAS ALSO VERY CONCERNED WITH GETTING BACK INTO REPUBLIC WITH ALL THE TFC AND LOOKING FOR TFC. I WAS NOT AS FAMILIAR WITH THE AREA AS I SHOULD BE AND ROADS AND REFS ARE SIMILAR AT BOTH ARPTS.