Every instructor ends up getting led astray by a student.
I know lots of folks hang their hat on the GPS these days, but when you don't have one, maps do the job just fine.
It sounds to me that you were new to the local area and unfamiliar with the airspace boundaries. That's the time when you need the map out and need to know where the airplane is on it.
'nuff said as you likely have absorbed the lessons, but a cautionary tale for the newer folks.