Groups shifting to the left in Preview

So I initially designed my app for desktop 1920x1080 view, but on running, I had to scroll to access parts of the app. I;m currently trying to redesign it to 1500x750 since that seems to be the optimal size for full-width view, though on some pages I still get white spaces on the side, and on some I dont. I’m super new to bubble, and I dont really get how the reponsiveness works.
I tried experimenting with a page, creating a Master group and such. It seemed to work except for moving the elements to the right on preview. Any help or advice would be greatly appreciated. Thanks in advance.