The difference between the last bid and $50 is only $28 dollars. In my opinion, just an opinion, you have to ask yourself if your reputation is worth $28 dollars.
Maybe there are more people like me who have been watching this auction, waiting for the right time to bid again.
Your original offer did state $1 increments, but sometimes this is taken to mean "$1 and up". Maybe it's just a simple language issue. Whether that is the case or not, I would stick to the sale as it is and learn the lesson, but keep your integrity intact.
As for ending the auction early, perhaps you will shoot yourself in the foot by doing that, and never find out how much you could have got, or worse.
I'm no expert in the rules and often make mistakes myself, but I like to believe that I won't sell my reputation ( at least not for many thousands $$$
)
Sorry to comment in a sale - but I'm an interested potential purchaser.
Mike