C152 PLT EXPERIENCED RWY INCURSION AT LGB.

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I DID THE VOR RWY 30 APCH INTO LGB AND LANDED. I WAS CLRED TO EXIT RWY 30 BY GOING L OR R ON TXWY J; AND THEN CONTACT GND. I WENT L ON TXWY J (FACING W; OR PARALLEL TO RWY 25L) AND CONTACTED GND. GND CTL CLRED ME TO RWY 25L AT TXWY D; BUT THEY DID NOT GIVE ME A HOLD SHORT OF RWY 25L AT TXWY D INSTRUCTION. GND CTL THEN TOLD ME TO MAKE A HARD L ONTO TXWY D (FACING PARALLEL TO AND OPPOSITE OF RWY 30; ALMOST PERPENDICULAR TO RWY 25L). I REPEATED THE INSTRUCTION TO MAKE A HARD L ONTO TXWY D; ALONG WITH THE INSTRUCTION TO TAXI TO RWY 25L AT TXWY D. I KNEW I WAS XING RWY 25L. I THOUGHT I WAS ALLOWED TO CROSS RWY 25L; SO I LOOKED BOTH WAYS. THERE WAS NO TFC SO I CROSSED RWY 25L ON TXWY D; AND PROCEEDED TO THE RUN-UP AREA ON THE OTHER SIDE; WHICH WAS STILL RWY 25L AT TXWY D. I NEVER LEFT TXWY D; I JUST CROSSED RWY 25L ON TXWY D. HAVING NOT RECEIVED A HOLD SHORT INSTRUCTION; I CROSSED RWY 25L AT TXWY D. THE PROB WAS DISCOVERED WHEN I CALLED GND CTL TO INFORM THEM I WAS CHANGING FREQ IN ORDER TO OBTAIN MY IFR CLRNC BACK HOME. GND CTL ASKED ME WHERE I WAS. I TOLD THEM; AND THEY INFORMED ME THAT A POSSIBLE PLTDEV HAD OCCURRED. I BELIEVE THE PROB WAS CAUSED BY A MISUNDERSTANDING BTWN GND CTL AND ME. TXWY D; TXWY F; RWY 34R; AND RWY 25L ALL INTERSECT AT ONE POINT. I BELIEVE THAT THE COMPLEXITY OF LONG BEACH ARPT ALSO CONTRIBUTED TO THIS SIT. I DON'T BELIEVE I DEVIATED FROM ANY INSTRUCTION; I JUST DID WHAT I PERCEIVED TO BE CORRECT. I DON'T BELIEVE THAT SAFETY WAS JEOPARDIZED BECAUSE I KNEW WHERE I WAS; AND I KNEW I WAS XING A RWY; AND I LOOKED FOR TFC BEFORE DOING SO. I DID NOT DEVIATE FROM A CLRNC INTENTIONALLY. THERE WAS A MISUNDERSTANDING ON BOTH PARTS AS TO WHAT I WAS EXPECTED TO DO; AND WHAT I THOUGHT I WAS INSTRUCTED TO DO. MORE CLR INSTRUCTIONS ARE NEEDED; AND WHEN GND CTL DOES NOT WANT YOU TO CROSS A RWY; A HOLD SHORT INSTRUCTION SHOULD BE GIVEN. LONG BEACH IS A LARGE ARPT AND CAN BE VERY COMPLICATED TO OPERATE ON. CARE MUST BE TAKEN ON ALL PARTS TO AVOID FURTHER SUCH OCCURRENCES.