I would love to help you with your code however I wanted to verify what you are creating. It looks like you are adding a contact one at a time using our Activities collection. Doing so would be against our TOS and could cause potential issues with your account. The Activities Collection is used when you are doing 20+ contacts at a time.
If this form is to create a join my mailing list application it would need to be setup as it would create a contact one at a time using the contacts collection which you can read about here.
Please let me know if you have any questions.
... View more