I checked your account.
The files are indeed uploaded to your account, but they are uploaded to a subfolder with the name 2. Maths Game (JS). So you will see your website is live on the URL followed by that sub path: http://mathsmultiplicationgame.42web.io/2.%20Maths%20Game%20(JS)/
If you don’t want the sub path to be required in the URL, simply move the files out of the subfolder and directly in the htdocs folder.
There is also a file index.html_ in the htdocs folder. If you want that file to be used, it must be called exactly index.html.