Add curve to SCNGeometry, and calculate normals

Question

I've created a polygon using SCNGeometry and I'm trying to add a curve to my shape, My code is:

let vertices: [SCNVector3] = [
SCNVector3Make(-0.1304485, 0.551937, 0.8236193),
SCNVector3Make(0.01393811, 0.601815, 0.7985139),
SCNVector3Make(0.2971005, 0.5591929, 0.7739732),
SCNVector3Make(0.4516893, 0.5150381, 0.7285002),
SCNVector3Make(0.4629132, 0.4383712, 0.7704169),
SCNVector3Make(0.1333823, 0.5224985, 0.8421428),
SCNVector3Make(-0.1684743, 0.4694716, 0.8667254)]

let indices: [Int32] = [Int32(vertices.count), 0, 1, 2, 3, 4, 5, 6]
let vertexSource = SCNGeometrySource(vertices: vertices)
let indexData = Data(bytes: indices, count: indices.count * MemoryLayout<Int32>.size)
let element = SCNGeometryElement(data: indexData, primitiveType: .polygon, primitiveCount: 1, bytesPerIndex: MemoryLayout<Int32>.size)
let geometry = SCNGeometry(sources: [vertexSource], elements: [element])

let material = SCNMaterial()
material.isDoubleSided = true
geometry.materials = [material]

let node = SCNNode(geometry: geometry)

The outcome looks like this:

Desired shape, adding 0.4 curve factor is:

Another question is how do I properly calculate normals for the surface given an array of vertices.

****** Update ******

When assigning geometry.subdivisionLevel = 10 I get a smoother round shape

But I still I can't figure out a way to add curve factor to the polygon shape.