SINGLE ENG ACFT ENTERS ABI CLASS C AIRSPACE WITHOUT AUTH DUE TO NAV ERROR

Narrative

I HAD NOT FLOWN A SMALL ACFT IN ABOUT 11 YRS. I FERRIED THE ACFT FROM ADDISON; TX; TO PORTLAND; OR. THE ACFT HAD A LORAN AND RNAV COUPLED TO AUTOPLT. WHEN I ENTERED THE RNAV INFO I MUST HAVE ENTERED THE WAYPOINT DATA WRONG. THE WX WAS VFR; BUT WE WERE BTWN RAGGED LAYERS AT THE TIME. I MADE THE MISTAKE OF NOT XCHKING THE RNAV POS. I WAS JUST N OF THE ABILENE ARPT BY ONLY A COUPLE OF MI WHEN I SAW THE ARPT. REALIZING MY MISTAKE; I TRIED TO CLB ABOVE THE AIRSPACE BUT COULD ONLY CLB TO 4500 FT; NOT THE 9000+ FT REQUIRED. I WAS NOT TALKING TO ANYONE ON THE RADIO. I FEEL THAT COMPLACENCY ON MY PART WAS THE CAUSE OF MY ACFT GOING INTO THE CLASS C. A NUMBER OF THINGS THAT I COULD HAVE DONE TO AVOID THIS ARE: GET FLT FOLLOWING; FILE IFR; DOUBLECHK ALL DATA ENTRIES. I THOUGHT WE WERE 15 MI TO THE S; WHICH COULD HAVE BEEN XCHKED VERY EASILY. I ALSO SHOULD HAVE HAD THE SECTIONAL OUT AND NOT JUST THE 'LOW ALT' CHART. TO SUM IT ALL UP -- SINCE I FLY TRANSPORT CATEGORY ACFT FOR MY JOB; I WAS OVERCONFIDENT WHEN I 'HOPPED' INTO THE SMALLER ACFT. THIS EVENT HAS BEEN A REAL EYE OPENER.