How do you know when the song that you're mixing is finished? Well, it's a lot easier than you think. There's two things that you need to do. Export the track as it is. Now save that and get mixing. Now, when you start doubting yourself. You don't know when it's finished. You're going round and round and round in circles. What you need to do is bring the original file into your session. And then, as if by magic, all of the differences will appear and you'll be able to hear if you've taken it too far or it's actually finished.