How to model a diffuser in solidwork?

Check "Circular Sketch Pattern" under "Sketch tool". With this function, this problem should be easy.
Here's a very simple demo using the data you provided.

  1. Step 1:

    Use your data to create the first one and use "Circular Sketch Pattern". Set the numbers of copies to 11.

  2. Step 2:

    Trim to get the sketch below. Then it should be nice and easy