What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
I have tried to submit a clone version of your form that I have created, I have integrated Authorize.Net in sandbox(test) mode. I was able to see the Thank You page after trying to make a test submission.
Here is the guide on How to Test Authorize.net Payment Tool on Sandbox Mode?
This might also help you in testing: http://developer.authorize.net/hello_world/testing_guide/
Let us know if you need any further assistance. Thank you.