Payment Form: How to allow users to pay using their PayPal account or mailing a check?

I have integrated a Paypal option on my registration form for those registrants that want to pay with that option.  Others will want to mail in payments.  But I noticed that since I added the Paypal feature the clicking Submit automatically takes them to the Paypal page for checkout.  Is there a way to code the Submit button so that it only goes to Paypal if they have chosen that option in a previous field?

No, it is not necessary, when you add the condition to show/hide the payment field it will act as indicated, for example if your users select pay with PayPal then the PayPal field will be shown and your users will be redirected to the PayPal payment page, but if they choose to mail a check they will not be redirected to PayPal. 

You only need to add the payment field to your form: 

Then take the total amount from your calculation widget: 

The last step is make the condition, show the payment field only if the option selected is "pay with PayPal account".

If your users choose "pay with my PayPal account" they will be redirected to the PayPal page, otherwise they will be redirected to the Thank You Page. 

Here is my cloned form of yours, I did it and it worked: https://form.jotform.com/60718483037963. 

Feel free to test it and clone it if you want, this guide will help you to clone my form: http://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL. 

Hope this helps.