ActionScript 3.0 :: Erasing A Circle From Bitmap Data?

I'm trying to create sort of an eraser to remove sections of a bitmap on stage.

I have achieved this by creating a MovieClip in flash that is a circle and exporting it as a Class called Hole.

Now I use this MovieClip to erase a circle section of the image using the following.

var mat = new Matrix();
var ct = new ColorTransform();
var hole = new Hole();
mat.translate(x,y);
image.draw(hole, mat, ct, "erase");

Now what im trying to do is scale the size of the circle depending on a certain variable but no matter what I try the scale doesn't seem to change and. The size seems to stay the same as I drew it in Flash. I tried adding the following line

hole.width = hole.height = size;

I even created a class file called Hole and the size as a parameter

var hole = new Hole(200);

This didn't work either it still appeared to have the same size. I have even tried altering the scaleX and Y values with no success.