project a curve onto a surface and divide the surface into two parts

I don't know if you have done such an effect? (Reference picture projectq & a.png)
1 is a closed curve
5 is a curved surface
Now I want to project 1 onto 5 and divide 5 into two parts.
I used the following code to achieve the effect in the figure.
2 is the curve of 1 projected onto the surface of 5, and 4 is the new surface generated from 2 and 5, the original surface 5 is divided into new surface 4 and surface 5. The problem now is that there is more curve 3, which is wrong. Do not you know why? Thank you all.
code show as below:

void CProjectToFace::build() {
    if (myAISContext->NbSelected() != 2) {
        return;
    }
    myAISContext->InitSelected();
    TopoDS_Shape shape1 = myAISContext->SelectedShape();
    if (shape1.IsNull()) {
        return;
    }
    myAISContext->NextSelected();
    TopoDS_Shape shape2 = myAISContext->SelectedShape();
    if (shape2.IsNull()) {
        return;
    }
    TopAbs_ShapeEnum shapetype = shape1.ShapeType();
    if ((shapetype != TopAbs_FACE) && (shapetype != TopAbs_EDGE) && (shapetype != TopAbs_WIRE)) {
        return;
    }
    TopoDS_Shape wireshape;
    if (shapetype == TopAbs_FACE) {
        BRepBuilderAPI_MakeWire makewire;
        TopExp_Explorer explorer;
        explorer.Init(shape1, TopAbs_EDGE);
        for (; explorer.More(); explorer.Next()) {
            makewire.Add(TopoDS::Edge(explorer.Value()));
        }
        wireshape = makewire.Shape();
        if (wireshape.IsNull()) {
            return;
        }
    } else {
        wireshape = shape1;
    }
	//	Calculate the projection surface closest to the projection curve
    TopoDS_Face projectface;
    GProp_GProps System;
    BRepGProp::LinearProperties(wireshape, System);
    gp_Pnt G = System.CentreOfMass();
    Standard_Real mindistance = -1;
    TopExp_Explorer explorer;
    explorer.Init(shape2, TopAbs_FACE);
    for (; explorer.More(); explorer.Next()) {
        TopoDS_Face face = TopoDS::Face(explorer.Value());
        BRepAdaptor_Surface aSurface(face);
        Standard_Real u1, u2, v1, v2;
        u1 = aSurface.FirstUParameter();
        u2 = aSurface.LastUParameter();
        v1 = aSurface.FirstVParameter();
        v2 = aSurface.LastVParameter();
        gp_Pnt aCenterOfFace;
        gp_Vec aVec1, aVec2, aNormalOfFace;
        aSurface.D1((u1 + u2) / 2, (v1 + v2) / 2, aCenterOfFace, aVec1, aVec2);

        Standard_Real distance = aCenterOfFace.SquareDistance(G);
        if (mindistance < 0) {
            mindistance = distance;
            projectface = face;
        } else {
            if (mindistance > distance) {
                mindistance = distance;
                projectface = face;
            }
        }
    }
    if (projectface.IsNull()) {
        return;
    }
	//	Project the projection curve onto the projection surface
    BRepAlgo_NormalProjection projection(projectface);
    projection.Add(wireshape);
    projection.Build();
    if (projection.IsDone()) {
		//	Convert projection results to wireframe
        TopoDS_Shape shape = projection.Projection();
        BRepBuilderAPI_MakeWire wire;
        TopExp_Explorer exploreredge(shape, TopAbs_EDGE);
        for (; exploreredge.More(); exploreredge.Next()) {
            TopoDS_Edge edge = TopoDS::Edge(exploreredge.Value());
            wire.Add(edge);
        }
        wire.Build();
        if (wire.IsDone()) {
            if (!wire.Shape().IsNull()) {
				//	Add the projected wireframe to the projection surface and split the projection surface
                BRepFeat_SplitShape splitShape(shape2);
                splitShape.Add(wire.Wire(), projectface);
                splitShape.Build();
                if (splitShape.IsDone()) {
                    TopoDS_Shape aNewShape = splitShape.Shape();
                    if (!aNewShape.IsNull()) {
						//	Stitch the new projection surface into a solid
                        BRepBuilderAPI_Sewing aSewingTool;
                        aSewingTool.Load(aNewShape);
                        aSewingTool.Perform();
                        TopoDS_Shape sewedshape = aSewingTool.SewedShape();
                        bool issolid = false;
                        if (sewedshape.ShapeType() == TopAbs_SHELL) {
                            BRepBuilderAPI_MakeSolid makeSolid(TopoDS::Shell(sewedshape));
                            makeSolid.Build();
                            if (makeSolid.IsDone()) {
                                issolid = true;
								//	Redisplay projection results
                                Handle(CADModelShape)::DownCast(myAISContext->SelectedInteractive())->Set(
                                        makeSolid.Shape());
                                myAISContext->Redisplay(myAISContext->SelectedInteractive(), true);
                            }
                        }
                        if (!issolid) {
							//	Redisplay projection results
                            Handle(CADModelShape)::DownCast(myAISContext->SelectedInteractive())->Set(
                                    sewedshape);
                            myAISContext->Redisplay(myAISContext->SelectedInteractive(), true);
                        }
                    }
                }
            }
        }
    }
}