Can I make sure that my form has one entry per person?

You can set unique submissions on your form, here are the available options: 

https://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form

https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question 

I hope this helps.