Excel export only includes those who have responded. It would be helpful to print the entire poll to see who has/has not responded yet. This info is sometimes shared with others to make a decision about dates to drop or add after the poll is distributed. There also should be a way to edit the poll for such changes without starting over.
It would be helpful to see a sample screen of what will be sent to people before you choose next. You should be able to go back and make changes to things before submitting the poll out to everyone.