How do it nonsymetrical filled
Looking at the images and file you provided I would say that you are skipping essential steps in your Fusion 360 training and this project is too advanced for your current skill level.
For example, you'd be better off adjusting the location and orientation of your canvas' such that they use the origin as a common point for alignment, which will help keeping your sketches and in result geometry oriented properly for further operations.
You are also using too many spline points to represent that curve.
@Anonymous wrote:
"..You are also using too many spline points to represent that curve."
What do you mean ?
I mean that you need to delete some of the spline control points and then adjust the shape with the location and tangent handles of the remaining spline points. You know what tangent handles are, do you?
@Anonymous wrote:
"..Looking at the images and file you provided I would say that you are skipping essential steps in your Fusion 360 training and this project is too advanced for your current skill level..."
The best science is practice, not theory. Unfortunately I have not found any tutorial that teaches how to do what I want, so I try to do it myself.
Surfacing is very technical and requires you to understand the theory behind splines and NURBS surfaces. That same goes for T-Splines. You can practice all you want to, but you will run into limitations if you don't understand the theory at least on a basic level. Here is a link to the Autodesk Alais theory Builders. That should help with that.