Firstly, try to get your terminology right before the hearing tomorrow. Details can be important, and much of what you have told us is factually inaccurate.
You have not been summoned to a Magistrates Court for a speeding fine, you have not paid a speeding fine, and, initially at least you did not plead guilty to anything.
You received a Conditional Offer of Fixed Penalty - which is an offer of an out of court disposal - paying a £100 fixed penalty and getting 3 points on your licence, in return for not being prosecuted for the underlying speeding offence. If you complied with the requirements to pay the fixed penalty and provide your identification details (name, address, date of birth, driving licence number) to the specified person(s) within the specified timescale, you cannot lawfully be prosecuted for the speeding offence. This is a penalty, not a fine, and you cannot enter a plea - you simply either accept the offer or you don't.
As the police have decided that you did not comply (which may or may not be accurate), they instigated court proceedings for the speeding offence (not for "the speeding fine" or not providing your licence details). Presumably you received an SJPN and entered a plea of not guilty, resulting in the matter being transferred to a magistrates court for a physical hearing? Mystic Meg has sadly died, and you only mention of a plea was a claim to have pled guilty to a fixed penalty offer, so we're going to need a bit of help here.
