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.
As I check your JotForm titled "Demo Builder",the form is already centered and looks good. Generally we recommend using iframe embed method to avoid any script conflicts on the website. Please refer to the guide below to get the iframe embed code for your JotForm.
However, it seems that it is required to upgrade Strikingly account to Pro in order to be able to embed HTML apps. If you are already having a Pro account, please try embedding the form using iframe embed and let us know if the issue still persists. It would be helpful if you can share the URL of the webpage where your form is embedded.
We do have the pro agreement and have to do source code rather than embed
due to tracking codes we have put into the source code of the form.
The URL is signup.getreviewtrigger.com.
Thanks for your reply and for providing the URL.
Please add the following CSS code between the <style> tag on the form source code. This should center align the form.
margin: 0 auto;
Here's a screenshot: