Clear your cache (if you don't know how, google it).
That happens because your internet cache, which is basically a little space allocated to storing temporary files like pictures and audio files and whatnot from sites you visit so that they can load more quickly after the first visit, doesn't recognise that the audio file changed.
If it did, it would've newly downloaded the audio file without the seconds of silence, but since it didn't recognise the change, it just loads up the old audio file with the silence that was stored back when you first uploaded the submission. Clearing your cache means that the cache will need to download the audio file again, whether it's the new one or the one with the silence.
If that doesn't work, then something went wrong in the uploading process.