Their small town eyes will gape at you
in dull surprise when payment due
Exceeds accounts received
At seventeen
The meaning is:
The small town Prom Queens expect their lives after school to pretty much be an extension of their existence as long as they continue on - they'll marry the High School jock, buy a house in the 'burbs close to mom, start a family eventually, blah blah...
Janis Ian is a lesbian, and always was. Her high school experiences are really less about being ignored by boys than her not putting out the "right" signals, i.e. wearing the right makeup, fluttering eyelashes, speaking in Marilyn Monroe tones to the boys she wanted, that sort of thing, therefore those who didn't understand who she was didn't expect much from her - she wouldn't find a handsome man, she wouldn't marry well, would probably die an old maid after a frustrated and unfulfilled life, etc.
These expectations were the ones that her schoolmates were prepared to bet on, i.e. these were the "payment due", in effect.
However, Janis always knew she was capable of reaching heights way in excess of anything her peers expected. She had already achieved experience and some success as a professional by the time "At Seventeen" was released. That success had "exceeded accounts received", so to speak, therefore those who weren't aware or clever enough to figure out who the real Janis was, found they were in debt, and watched on with expressions of amazement, their "small town eyes" agape.
That's what I reckon, anyway.
