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.
There is no direct tool to resize the scale of your background image on the advanced designer, but you can insert a CSS code in it. This guide will tell you how to inject CSS codes into your form: https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes
If you can also give us more information on which background you're referring to and what is your projected size, perhaps we can give you the CSS code to use.
We'll look forward to your update.