To be able to solve a width problem on iOS, you must first identify the type of kit you are using to manage your Webview on iOS: UIWebView or WKWebView.
If you use UIWebView
The "scalePageToFit" setting is disabled by default, and therefore does not interpret the viewport. You must enable it so that the display is set across the entire width and the game is not cropped. However, Apple recommends using WKWebView.
If you use WKWebView
The "scalePageToFit" setting is normally supported by default, unless you have disabled it, in which case you will need to enable it again to fix the problem.