Grain effect...

Hello all

I try to put a grain effect texture on my shapes.

I've followed the instructions found on the web.

Step 1 : make a circle (for example)

Step 2 : copy the circle / paste in the same place / full it with no colors / make a gradient

Step 3 : apply grain from the effect menu > textures > grain

It seems to be simple but when I apply the grain texture, the edges are pixellized as you can see on my picture. The edges are not smooth... It's horrible !!!

Do you know why ? What did I do wrong ?

Many thanks for your answer !!!

Nicolas