Why is this "da ceremonia" and not "na ceremonia"?
It can have the same meaning. But if you say "da cerimônia" doesnt imply you have an active participation there, you will just attend. "Na cerimônia" can take the meaning you will have to give a speech, for instance.
Thanks for the explanation!
How about 'I don't want to attend the ceremony'?
Another possible meaning.