Preview before submit button is not showing on my form

Preview before submit button not showing because you do not have submit button. When you add submit button to your form Preview before submit button will be visible.

Submit button is located under Form Tool tab. Simply drag and drop it inside of your Form Builder. 

I have cloned your form and added submit button to my cloned form. 

Here is my cloned form: http://form.jotformpro.com/form/52412678171960? 

Hope this will help. Let us know if you need further assistance.