I see that it’s scaling to both 100% width and height so it will get stretched depending on the screen/window’s aspect ratio. Since the loading screen is always rendered in webkit you should set the background image using CSS and use the CSS property “background-size:cover;” to scale it. This will crop so you’ll need to have your text and logo as separate images absolutely positioned above.
The HTML code behind it isn’t good, you have missing opening and closing tags and some in the wrong order. e.g. you have a </html> tag inside a </style> tag and no opening <html> or closing </body> tags. Web browsers are really forgiving.
Also you are using flash for audio which isn’t necessary, you can use the HTML5 audio element. Lots of people prefer loading screens not to play music as they have their own.
The image is about 1MB big so it may take a long time for it to show up, consider compressing this a bit.
Also a loading animation might help, also look at Garry’s default loading screen so you can show progress on downloading files.
Hope this helps.