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 checked your from and noticed that the font size is the same when opening it on the Form Builder and loading the direct link, the current font size is 12px.
Loading the direct link:
I have also checked the custom style that you have added in your form and there is not any code that could be affecting this, or perhaps you noticed this and removed it; however, if you want to change the font size for your form you can do it by opening the preferences:
Then you will be able to change the font size for your form:
Other way to change the font size is injecting this CSS code:
This guide will help you to inject the code: http://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes.