We are about to use jotform for a race registration. Can we allow users to return to an incomplete registration form?

You could use our feature to Save form and continue later. That will allow your customers to start filling your form and then continue later. You could also send your users an autoresponder with edit link in it, so they can edit their submission and send again. You can check this guide on how to do that.

Please let us know if you had something else in mind maybe.

Thank you!