I'm not sure if this is what you mean, but if you adjust your background image a little it almost perfectly lines up with a circle. Here I have a cylinder with 16 segments and it matches the shape of the headphones:
I don't know what tutorials you're using but I would suggest a few things to make it easier:
- cut the headphones in half and use a mirror modifier. Then you only need to model half of it. If you want asymmetry you can add it later!
- if you're using a subdivision modifier anyway, try to use as few vertices/edges as possible. The more you have the harder it is to make changes.
- if you really want to continue with what you have, I would create a set of circle meshes and snap the vertices to them. Here I created 3 'circle' meshes with 64 vertices and lined them up with the headphones. You could snap your vertices to those edges - but that's a fair amount of work.
Hope this is helpful, or at least points you in the right direction.