Build a face from a surface and a wire

Hi to all...i've a little problem in building a face from a face and a wire with BRepBuilderAPI_MakeFace.

The step that i run are the following:

first a create a BSplineSurface. This surface is created from a matrix of point and is square. Now i want to cut the bounds of this surface with a custom polygon. For make that i build a wire and project it in direction of the surface with BRepProj_Projection. The result of is a one or more compound of edge and with it i build a face with BRepBuilderAPI_MakeFace. At the end i do a ShapeFix_Face.

Now start the problem.

In most cases BRepProj_Projection return multiple compound. Now from this how a can build a single closed wire that lie on my surface??

I some cases when the result of the projection is a single compound the face constructed from the wire of these edges is goog...(id i dump the topological structure of it there are the edgese, wire and vertex) but the triangulation of it return a null triangulation. Why???

Thanks in advance for your help. Thanks!