Firstly, a simple check: Is it possible that you are editing the width and height as mentioned in the editor as the ‘Canvas height’ and ‘Canvas width’. That will only impact the size of the page you are looking at in the Studio Pro and won’t impact the popup you see when you actually run the page. There is a section on the bottom of the editor labeled ‘Popup’ where you can set width and height of the rendered popup.
Assuming you are setting things in the correct place, you may need to crack open the f12 browser console present on most browsers and inspect the popup on the page. It could indeed be that something is overwriting the height and width settings of that popup. It may live in the css of your app. It could be in hard-coded height and width css values on specific containers within the popup itself. Once you know the source of the height and width from the browser console, you can learn where you need to make the change.
You can change the pop up size in the properties section of the page. You can achieve it by changing the width & height of the page.Please find the screenshot for your reference.
I hope this helps you.
In addition to what the others already said:
Make sure to reload the page in your browser. Sometimes it seems not to be refreshed as it should. Reloading everything can help.