unity - TopDown Island Generation

I am trying to generate an island using Simplex Noise. To actually make a island shape i used Amitp's answers to the following questions:

1.Fast, simple procedural 2d island generation

2.Generating random Pools or lakes

Using them i have snippet of code for generation:(width/height is 128)

for(int y = 0; y < HEIGHT; y++) {
        for(int x = 0; x < WIDTH; x++) {
            // amitp's solution
            Vector2 vec = new Vector2(2 * x / WIDTH - 1, 2 * y / HEIGHT - 2);

            float d = Mathf.Sqrt(vec.x * vec.x + vec.y * vec.y);
            //
            float noise = Noise.Generate((float)x / WIDTH * 10, (float)y / HEIGHT * 10);

            // amitp's solution again
            mapData[x, y] = noise > 0.3 + 0.4*d*d ? noise * 10 : 0.0f;
            //

            colors[x + y * WIDTH] = new Color(mapData[x, y], mapData[x, y], mapData[x, y]);
        }

    }

This gives me the following unwanted result:

How do i get fix it to generate properly?

Lastly i'm using Unity.

***EDIT:

Fixed/Changed a couple of things and now i am getting this(still not what i want):

with this changed code:

for(int y = 0; y < HEIGHT; y++) {
        for(int x = 0; x < WIDTH; x++) {
            // amitp's solution
            Vector2 vec = new Vector2(((2 * x) / WIDTH) - 1, ((2 * y) / HEIGHT) - 1);
            float d = Mathf.Sqrt((vec.x * vec.x) + (vec.y * vec.y));
            //
            float noise = Noise.Generate((float)x / WIDTH, (float)y / HEIGHT);

            // amitp's solution again
            mapData[x, y] = noise > 0.3 + 0.4*d*d ? noise * 10 : 0.0f;

            //

            colors[x + y * WIDTH] = new Color(mapData[x, y], mapData[x, y], mapData[x, y]);
        }
    }

Answer

I suggest this aproach. Let fs(x,y) be your simplex noise function. Let's introduce a second function : f(x,y) = ((float)Math.Sin(((float)x/(float)WIDTH) * Math.PI) ) * ((float)Math.Sin(((float)y / (float)WIDTH) * Math.PI) ) or any function that rassemble the following and that gives values from 0 to 1:

at this point take your simplex noise fs(x,y) :

and multiply per f(x,y) you get something like this :

finaly apply a colorgradient to obtain something like :