Why does my song sound different when I upload it to YouTube?

I use fl studio to make tracks.You have to render the song in the higest quality there is.When you export it there will be an option for the mp3 bitrate put the bitrate to 320kb.If you have allready done that then export the song into a wave file then convert the wave file into MP3.Also when you upload a song to youtube the video and sound gets compressed even more so it loses sound quality.Hope it helped fellow music maker =)