How to set up wide aspect ratio for html5 hosting on Itch.io?

Hi,
I want to make a “Google Doodle” styled interactive media “game” to embed into a website, so I’m using Unreal Engine 4.23 for its HTML5 building abilities.

I want to use UE because I’m very familiar with blueprinting and widgets and it might be easier for me in the short run. BUT, I’m having an issue figuring out how to get the aspect ratio to work the way I want.

Aspect Ratio:
Because I’m seeking a banner-styled google-doodle-esque end product, I’m hoping for a 3:1 aspect ratio. However, I’m not sure exactly where to set that up in 4.23. I’ve tried the camera in the player character, and set the

Cam setup:
I’m using the default 2D map, and my first instinct was to set the camera up for using a 3:1 aspect ratio.

Player Advanced Settings:
Next, I went to the advanced settings in the player, and set the aspect ratio to 3:1. When I hit the play button, I see the aspect desired aspect ratio. However, I don’t think this has any affect on the actual game, since it’s in the “level editor” portion of the settings.

ITCH:
When I upload the packaged html5 game to Itch.io, I specify the viewport settings to 1200 x 400 (3:1)
UE_AR_03_Itchviewportdim

Final Look:
But when I play the game in the browser, I see a game that still has the top/bottom bars.

Thanks for any help or thoughts!