Thankyou very much

HELP I parked my car in a layby in London N7 on Wednesday to go to a football match, there was no signs as far as I could see to say I couldn't park there (thats beside the point) when I came out I had a ticket but on looking closer the registration had been written wrong, I don't know if a camera was also used, should I pay or hang on and hope for the best. If I wait then I will have to pay the full £100 but if I pay before the 14 days is up it is only £50. Thanks for any help anyone can give Bruce