Hi Sherwin,
Just to clarify something on your side, you also did not officially say you are sponsoring the event, you just said you would. Where was this "officially announced"? Also on the thread you just asked if the 3rd was a date that suites everyone, that does not imply commitment to sponsorship nor the organization of the event itself. Burgy and Sankekur have been working on the organization of the event. So when you saw Burgy's post why not speak to him in private and discuss whether you could assist in sponsorship and organization or that you had a plan to assist why the cancer shavathon?
If you had organized such a "big event" in the first place and you had already organized trophies and with the Cancer Shavathon why keep it a secret? Why not announce it on the forum as soon as possible so that as many people can get involved? Why organize everything and not tell anyone? Sounds very fishy. Personally i think you just trying to give yourself credibility with the event so that people will feel compassionate towards your cause especially with a cancer shavathon.
You are a forum sponsor and although there may not be hard and fast rules about events and invitations surely this would be the first place you would mention such a "big event"?