So long as you are in line to vote at the time the polls close you will be allowed to vote. 

Yes. Iowa law allows for Election Day registration if you are able to provide proof of identification (i.e. valid photo ID) and proof of residency (i.e. utility bill with your name on it if your ID has an outdated address on it). If you are unable to provide one or both of these you are allowed to bring someone with you to attest that you have the right to vote.