And how can i fill this with a color?
View attachment 78542
It doesn't look very nice to me.
For filling, I wrote you to figure it out for yourself.
You saw how I made the wave here ...
I give you another help, you put too many points in the SPLINE and you have arranged them badly it doesn't look like a wave.
Third aid. You need only the points but you don't have to trace them like in my example
Now I have told you too much, you are very good and I am sure you will understand by yourself