Well, unless amended, you stand a good chance of beating this it would seem. Assuming the officer doesn't testify that you were EXCEEDING 100.
On the citation where there is a box that indicates the speed you were traveling, does that also indicate "100"? Or, is there some other speed indicated somewhere on the cite?
Even with the testimony, imagine the cross.
Q: "On the date of the citation at the time of the purported offense, you wrote "approximately 100", is that correct?"
A: "Yes."
Q: "Today, three months later, your testimony here is that the OP was traveling 102, is that correct?"
A: "Yes."
Q: "What caused you to believe the OP was traveling 102?"
A: "I clocked him with my speedometer (Or, whatever), for such and such a time."
[Q&A establishing why measuring device or opinion is accurate.]
Q: "Why did you not put the correct speed on the citation?"
A: "It was the correct speed. It was approximately 100."
Q: "Is the purpose of the citation to help you refresh your memory about the events of the date?"
A: "That and to start the charging process for the courts."
Q: "So, it is your testimony today you wrote "approximately 100" on the citation to help you remember he was traveling 102?"
A: "Yes."
I'm thinking I'd have a reasonable doubt.