You have been caught fair and square by the sound of it and where you stand is that you have to pay the fine. it's not any defence to say well i would have blocked the road instead, because you should not either block the road OR park on the pavement where there are no lines allowing you to do so
Anb analogy for what you are saying is that if you hit someone over the head and cracked their skull that your defence would be "well it was worse for me to kill him , and i didn't do that therefore you should let me off"