If you are going to bow out, it would be much better to do it sooner rather than later - so as not to leave the organisers in the lurch. Giving a public speech would be a big deal even if you were fine with other "regular-life" activities - so I don't think you should beat yourself up over it.
If you think you can do it, then I'd strongly recommend getting the talk together well in advance, and practice it a number of times - the more often, the better.
I'd second the comment about Toastmasters, although that might be more useful for preparing for similar events in the future, rather than for the immediate one.
If you think you can do it, then I'd strongly recommend getting the talk together well in advance, and practice it a number of times - the more often, the better.
I'd second the comment about Toastmasters, although that might be more useful for preparing for similar events in the future, rather than for the immediate one.