An elementary way to make it (or something resembling) is to make the surface by revolving an ellipse 180 degrees (or a half ellipse 360 degrees). Then one can extrude it to the normal direction to the wanted thickness. Many programs also allow creating a shell with wanted thickness around a solid. In the most simple programs one must revolve a profile which already has the wanted final thickness.
The holes can be drawn in plane and extruded to bars. Subtract them from the shell and that's it - add only the ring.
Another a little different approach is to make one petal and bend it. Bending a piece can be tricky or it's not at all implemented in simplest programs. I have a simple one which has a kind of bending .The next example is made there (=a low cost program named Moment of Inspiration, "MoI")
The bending in MoI is only a geometric trick. MoI is definitely not a valid metal engineering tool because it has not a slightest idea of how real metal would behave. That capability would need some real money to be purchased.
See the next image:
The planar petal is a XY-plane surface limited by 4 circular arcs which are joined. The curve in the right is a quarter of an ellipse. That will be rotated 90 degrees and used as the bending profile.
The ellipse arc is rotated to YZ plane and a corresponding reference line is drawn on the petal in XY plane:
MoI has geometric deformation named "Flow" which forces the piece under deformation so that the reference line becomes the wanted profile. Here's the result:
The original is still there. I keep (and hide) it for safety because the program is not a parametric CAD.
Extrusion makes this solid:
It's extruded to Z-direction. It's not physically realistic, it's jumping over where the fence is lowest; See NOTE1.
An upside down copy is made. The pieces are placed to overlap a little:
The final shape (minus the ring) can be made by making rotated copies and an union of them. I rotated 30 degrees/petal to make a little less dense version:
The edge strokes disturb. Without them one can see better how the surfaces fit:
Here's a high zoom into show the joints:
One can see that there's a little error at the joints. That's because the petals have only a single curvature, their overlaps cannot form a smooth continuous surface, there must be steps. The surface normals point to different directions where adjacent petals meet.
NOTE1: Extrusion to surface normal direction would be more realistic. The easy way to get it is to extrude the planar version and to flow (=bend) the already extruded version:
That makes easily exactly fitting cusps, but the crossings in the middle of petal edges have still the same steps as in the previous version:
That impossibility to make a smooth surface by joining rotated single curvature petals can be the cause of your error message. I cannot verify it (= no Creo nor other high cost professional CAD software available)
Making a smooth surface by joining rotated petals is possible if the petals have both needed curvatures. The easiest way to get it is to project the planar petal shape onto a revolved surface:
The circle is the reference surface. The dome below it is a revolved quarter of an ellipse. This is the result of the projection (project is a mode of Flowing):
Extruding and making rotated copies gave this result:
This is a smooth surface, as expected. High zoom in doesn't show any steps at the joints:
