JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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 page and the border looks like the inset border, which is not part of your form, but part of the iframe.
Further, there is a chance that your form might have issues and hang on submission as it's using the wordpress embed code, which seems to be a bit buggy. Instead, may I recommend to use the iframe which it also already includes to remove that dark border on the left and top. You can refer to this guide on how to get the iframe embed code: https://www.jotform.com/help/148-Getting-the-Form-iFrame-Code
If you have questions, please let us know.
Worked like a charm! Thanks!