Hi Joeri,
I think you would get better results with the spline tool...
After you get the right shape:
1. Use the magic wand to create a fill;
2. Also with the magic wand create a hole with the bath thickness;
3. Cut half of the shape to build a complex profile;
4. Use this complex profile to do the half rotation along the axis;
5. Save a 3d view with the correct orientation.
It seems that the original shape is also stretched along the z axis... To achieve this use another zzyzx value to get a perfect result and save it as an object again with the final zzyzx value.
p.s.: Use a cross to help you built the oval shape... making the four nodes of the spline be coincident with the cross
HTH