You went past the signs twice so by the letter of the law there are two contraventions.
However your best bet IMO is to make a plea for discretion requesting that they allow you to pay one PCN at the discounted rate. This is the only scenario where I'd suggest sending a letter in the post, because if they only log it against one of the PCNs you then get the other one cancelled based on a failure to consider.
Also if you have any meaningful mitigation please tell us now.
Lastly please re-post the remaining pages of the PCN, for some reason they don't load up. I suggest you just upload them to your google drive folder and let us know when that's been done.