Your form accepts multiple submissions by default. If you want to prevent your form submitters from making multiple submissions then here are your options.
Don't Check — This option means the form will not check for duplicate submissions.
Use IP address — This option is a strict check, which means the form checks whether the submission came from the same browser and IP Address. Please note if you select this option then people belonging to the same network such as school and colleges might not be able to make submissions.