If you’re not on the registration list you should be able to vote by provisional ballot.
First verify with the polling official that you are in the right location - if it turns out that you were not in the right place, in some jurisdictions the provisional ballot will not be counted. Your provisional ballot will be kept separately from other ballots. Election officials will examine your provisional ballot after the polls close and determine whether you were in fact eligible to vote according to state law.
Different states have different policies regarding the counting of provisional ballots. There will be a free notification system, such as a telephone hotline, to allow you to find out if your ballot was counted and if it was not, why not. Poll workers will provide you with written information describing how to access the free notification system. If you are not given this information, go to the Election Official Directory. Choose your state and region to find the contact and address of your local election official to find out about your registration.