Mask Issues

I'm brand new to After Effects and have been diving into tutorials in an attempt to learn some of the functions. I may have bitten off more than I can chew however. I've followed this video copilot sun tutorial to the letter and have been stopped in my tracks by something that seems like it should be simple. I'm trying to create an elliptical mask over a fractal noise layer and feather it. Sounds straight foreword right? When I apply the make, though, the circle is not a smooth round ellipse but rather a wobbly looking amoeba shape. And when I feather, rather that smoothly blended edges, it gives me a weird glowing distortion around the edges. Very frustrating and after hours of searching, an answer continues to elude me. Please help! The tutorial in question  can be seen here Solar Atmosphere Tutorial - YouTube and the issue occurs to me at 16:35 into the tut. You can see that he adds an elliptical mask, it's a perfect oval shape, and he feathers it... that is not the case when I do it.