Alleged 13km over speed limit in a 50 zone?

I recently got a speeding fine on Annerley Road just near the McDonald's. I don't normally drive in the area and thought it was a 60 zone as per the rest of the road further on. The ticket alleged that I was travelling at a speed of 63km, that's exactly 13km over the limit which means it's a level 2 fine (almost double the cost of a level one). I always use my cruise control (which was set on 60km at the time) so I find it difficult to accept that it was indeed 63km and not 60 or 61. Don't get me wrong, this is not an attempt to evade a speeding fine but fair is fair. I admit that I have unknowingly broken the limit in this particular scenario but I do NOT concede to being 13km over. I was wondering if anyone else has had any experience with disputing a similar situation in court and how it works/played out? Am I wasting my time? Will the system favour the police? I'm not one to complain about this sort of thing but I honestly feel that this is unjustified. Constructive input is appreciated.