UNAUTH PENETRATION OF CLASS B AIRSPACE.

Narrative

I WAS ON MY WAY TO DO A ROUTINE FLYING/TFC RPTING FLT. AS I WAS CLRED INTO THE BALTIMORE CLASS B AIRSPACE; THE CTLR MADE SURE TO SAY TO STAY OUT OF THE CLASS B SURFACE AREA (5 NM RING) AROUND BWI AS THE CTLRS DO EVERY DAY. A FEW MINS LATER; MY DME SHOWED 5 NM; SO I IMMEDIATELY WENT THE OPPOSITE WAY. THE CTLR SAID THAT I WAS 3 MI AWAY AND TO DEPART THE AIRSPACE; WHICH OF COURSE; I DID. APPARENTLY; ACCORDING TO HIM; I HAD COME IN THE SURFACE AREA EVEN THOUGH MY DME SHOWED 5 NM OUT. WHEN I DOUBLE-CHKED WITH OUTSIDE REFS A SECOND LATER; I REALIZED I WAS QUITE CLOSE TO THE ARPT WHICH MEANT I PROBABLY DID ENTER. WHY AND HOW DID THIS HAPPEN? I AM A VERY ALERT AND CONSCIENTIOUS PLT; WELL; LOW VISIBILITIES PREVAILED (ABOUT 3-4 MI IN HAZE) WHICH MADE IT DIFFICULT TO SEE. ALSO; SINCE I WAS ALSO TFC RPTING; I GOT CARRIED AWAY AND NEGLECTED TO MAKE PLTING MY FIRST PRIORITY! THAT HASN'T HAPPENED AGAIN. ALSO IF YOU ARE VFR; YOU SHOULDN'T DEPEND SOLELY ON INSTS; YOU SHOULD VERIFY AND KEEP TRACK OF YOUR POS VISUALLY. I HOPE THIS WILL HELP FUTURE PLTS TO ALWAYS KEEP AWARE OF THEIR POS AT ALL TIMES.