Change stage dimensions without affecting animation

Hello,

I'm not a developper and am new to Animate so be gentle. I created a simple animation in an HTML5 Canvas Doc with multiple timelines and motion tweens. I created the size based on the artwork provided to me. I'm just exporting a .gif so the animation can be shown to the client and I was asked to just make the document size bigger and square. I know I can export at a different scale and that's fine, but how do I change dimensions of the document/stage/canvas without affecting the animation itself?

I locked my layers, changed the size of the stage and kept everything centered. It looks perfect but when I play the animation in the new size, all of the positioning of the objects are wrong. Things that used to stay centered now fly in from other directions. I dont want my animation to change at all - simply change the stage for presentation purposes. Possible? Or can I do it as part of an export? 

Files attached for reference. Thanks!