The good news is that it should be fairly straightforward to sort out (although it will require attendance at court).
You will swear a Statutory Declaration to the court after receiving the appropriate warnings from the Clerk about the need to be truthful. That will mean that the convictions and penalties are removed and things start again as if you had not been convicted.
The speeding offence will then be put to you again, for which you will plead guilty.
The Prosecutor will then offer no evidence for the s172 offence, effectively withdrawing it.
The court will then fine you for the speeding offence, order that your licence be endorsed and make an order for the collection of the fine.
Job done.