How do I stop a person from registering twice on my form?

You can take advantage of our unique submission feature to block multiple submissions from one system of one IP address by setting the "Loose check" or "Strict Check" respectively.

Guide: How to Set Unique Submissions on a Form.

You can also use our unique question feature to prevent from submitting duplicate submissions.

Example: You can set one of your forms question (like email or questions) to be a unique question. This will not allow a user to use the same answer or email address to submit your form.

Guide: How to set Form Limits Based on a Unique Question.