They may have been spending time repairing your mix though. I agree with el-bo that you would benefit from learning some basic mixing skills. There are a ton of good mixing tutorials for all types of music online, and they can make a huge difference to how a track sounds once you learn some useful techniques.
Also, you might want to not just rely on headphones - they will give you one view of a mix, but it really helps to be able to crank some good monitors and listen to that as you mix.