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I believe this is the form (http://www.jotform.co/form/62013573491856) you're working to, right? Also, this is the Date field you're describing, right?
In order to fix that, please "Expand" the field. Just right click it or click the gear/options icon and then select the "Expand" option.
Also, please try enabling the "Make this form mobile responsive" in the Form Designer.
Here's the result:
Related guide: How-to-make-forms-mobile-responsive
Hope that helps. Thank you.