editing a poll for issues such as grammar correction has always been a issue with polls. Even if nobody has voted yet.
The only way is to delete the post and start over.
Maybe someday we will get at least a preview page before submit.
The way it was explained to me is that you can't edit a poll after it is started. Since it would not be fair to the users if say you change the questions in the interim. Which makes sense but !!!!
But we should have some way of a preview to at least make sure it is what we want and edit before posting and allowing votes.
