Manipulating mesh vertices

[pintariching]

I wanted to manipulate the vertices of a mesh with WASD keys and press space to switch between the vertices. Here is a repo of the project if anybody wants to check it out.
The problem I have is the following:

I have the mesh and the vertices defined like so:

let mut positions: Vec<[f32; 3]> = Vec::new();
positions.push([100., 0., 0.]);
positions.push([100., 100., 0.]);
positions.push([0., 100., 0.]);
positions.push([0., 0., 0.]);

// create a new mesh and set the positions
let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
mesh.set_attribute(Mesh::ATTRIBUTE_POSITION, positions.clone());

// set the mesh triangle indices in a CCW direction
mesh.set_indices(Some(Indices::U32(vec![0, 3, 1, 1, 3, 2])));

then when I create the MaterialMesh2dBundle entity I insert a component

#[derive(Component)]
struct VertexPositions {
  positions: Vec<[f32; 3]>,
  selected_vertex: i32
}

Then later in the code I reference the mesh and positions and change the vertex position of a mesh and update them like so

mesh.set_attribute(Mesh::ATTRIBUTE_POSITION, vertices.positions.clone());

Now I have a problem I can't seem to solve. I can move the top right vertex with the coordinates [100., 100., 0.] without a problem.
However the other vertices are giving me problems. Both the top left [100., 0., 0] and bottom right vertex [0., 100., 0] can only move in one direction and the bottom left vertex [0., 0., 0.,] doesn't move at all.

The code to move a vertex on each update looks like this:

if keyboard_input.pressed(KeyCode::D) {
  // 0 is for x, 1 is for y and 2 is for z
  vertices.positions[selected_vertex][0] += 50. * time.delta_seconds(); 
}

I would like to move all 4 vertices of the square but for some reason they don't want to.