How to add products to a payment form?

I create a second item but every time I change the item name of item 2 it changes the name of item 1.

I checked your form and I was able to change the name for one of the products, please see the screenshot: 

You are always able to add the products that you want, I would like to share you this guide where you will find more information about setting up your order form: http://www.jotform.com/help/165-Setting-Up-Your-First-Order-Form. 

I noticed that you have added options to your products so this guide could help you as a reference: http://www.jotform.com/help/225-How-to-add-options-to-Payment-Forms. 

Do let us know if the issue still persists and please, provide us the steps to replicate it so we will make some tests.