Hi RickyLah.
While BlackForest has earlier pointed out the High Court case of Yong Heng Hew stating that littering is strict liability, I would like to point out a few things.
1. In the case, CJ Yong stated that for a person to be convicted of a strict liability offence, a blameworthy element needs to be shown. This means that even though s. 17(1)(f) of the Environmental Public Health Act, which you have been charged under, includes "leav[ing] behind", unless you have done this DELIBERATELY, as far as the law stands, you are NOT guilty.
2. The law of evidence places a burden of proof BEYOND REASONABLE DOUBT on the STATE. As such, AS FAR AS THE LAW IS CONCERNED, the moment you step into court, and DENY the NEA Officer's account, and state what happened to you to the judge - course, humbly and clearly - the NEA Officer must prove that it is MUCH MORE LIKELY that his account is true as opposed to yours. As such, if the story you have related is true, it is your legal right, and in fact, the best course of action, to fully and frankly state what occurred to the judge, and allow justice to take its course.
These things considered, it is in your best interests to appear in court and deny what the NEA Officer alleges. State the facts truthfully and clearly, and adopt a humble demeanour toward the judge.
At the same time, you should continue your efforts in your appeal to your MP, as well as write in to the Straits Times. While creating public awareness will not do you any good in a court of law, and no petitions can be admitted, as they are what is known as "hearsay" evidence and not relevant to proceedings, this can certainly do you know harm, and allow your injustices to be heard.
All things considered however, you may wish to consider simply paying the fine. This is no substitute for professional legal advice. More importantly, professional legal advice would probably cost you at the very least, several hundred (if not, at least $2000 in reputable firms). Free legal aid is available, but has a long wait and may not necessarily involve representation for such a small case.
All the best, and good luck!