my object is split into two. Last time I got rid of this problem by making normals consistent, but this time it doesnt work. I have a Mirror Modifier on the objecgt, but not applied yet. Thanks for your help!
Your mesh is a nightmare to edit, because you applied the SubSurf modifier. You shouldn't do that unless you've got a good reason !
The next step is to add a Subdivision modifier again, so the mesh will look smoother. A Level of 2 or 3 is more than enough.
For the mesh to look even smoother, but without adding more faces, you can go in the Object menu and select Shade Smooth.
I would suggest to read this Topology Guide (the whole site is quite interesting) if you want to improve this useful skill.