Did you sign an invoice and did you get a receipt? If so, keep it and send a copy if there should be any inconvenience. I doubt that there will be some kind of aftermath, though. It's probable that they didn't charge your CC until the ticket was "officially" issued (aka the letter you posted). Wait another month and see. If they'd want more moneys from you, they'll tell you

A vital correction to my first post: it's 25 km/h or more within 2 years, not 31 km/h, sorry.

EDIT:

Damn, even your speeding ticket pictures look awesome, kudos!

Your Sea Dweller pics made me crave and finally buy one

the receipts look alright, keep them for file reasons. The second page of the letter also says that the sum was already paid for by security bond, so the payment you did on site is alright in the police's books. No need to worry.