PLT OF A PIPER COMANCHE; PA30; FAILED TO FOLLOW FLT PLAN CLRNC DUE TO NOT HEARING THE RTE CHANGE GIVEN DURING CLRNC DELIVERY PRIOR TO TKOF.

Narrative

I DEPARTED LGB ARPT WITH AN IFR FLT PLAN ON FILE TO MY DEST. THE PLAN; USING LOW AIRWAYS; HAD BEEN CREATED USING FLT PLANNING SOFTWARE; AND THE VORS WHICH DEFINE THE RTE HAD BEEN PREVIOUSLY STORED IN A FLT PLAN IN MY IFR APPROVED GPS. IN ADDITION; THE PLANNED RTE HAD BEEN HIGHLIGHTED ON MY LOW ALT ENRTE CHARTS. AT LGB; CLRNC DELIVERY PROVIDED A CLRNC THAT DIFFERED FROM THE EXPECTED RTE. AFTER RADAR VECTORS; THE CLRNC NAVIGATED TO EED (NEEDLES); THEN 'AS FILED.' THE LGB CLRNC DELIVERY CTLR; WHO WAS VERY BUSY WITH MULTIPLE IFR DEPS; GAVE THE CLRNC VERY QUICKLY. I COPIED THE CLRNC AND READ IT BACK AFTER SOME DIFFICULTY AND CORRECTIONS IN READBACK. I THEN UPDATED THE RTE OF FLT IN THE GPS AND HIGHLIGHTED THE NEW RTE OF FLT ON MY ENRTE CHART WITH A NEW COLOR OF HIGHLIGHT. THE ATC CLRNC INCLUDED V208 FROM TRM TO EED. HOWEVER; I ONLY MARKED (AND PROGRAMMED IN THE GPS) V208 FROM TRM TO TNP; AND THEN FLEW V264 FROM TNP TO PKE AND V135 FROM PKE TO EED AS ORIGINALLY PLANNED RATHER THAN V208 FROM TNP ALL THE WAY TO EED. WHEN E OF TNP; ATC INFORMED ME THAT I WAS 15 NM S OF COURSE; AND WE DISCUSSED THE CLRNC. I THEN REALIZED THE ERROR IN UNDERSTANDING THE EXPECTED RTE OF FLT. ATC THEN CLRED ME TO MY FLT PLAN AS I HAD EXPECTED IT; AND PROCEEDED WITHOUT FURTHER INCIDENT. ATC COMMENTED THAT MY RTE OF FLT HAD WORKED OUT BETTER; AS IT HAD A LOWER MEA AND THERE WAS ICING AT HIGHER ALTS REQUIRED BY THE RTE OVER V208. THERE WAS NO TFC CONFLICT.