Honestly I don't know how I got it, either time. I KNOW I missed more than two or three of the stupid stars both times. It is a giant mystery and I feel totally suspicious of it.
I tried & tried & tried and never got it. Finally gave up completely & just went for fun. Got it the first time. I now know it has some give built in. Like, if you miss a star, go back and get it, then continue & it'll award it to you. i.e. If you miss Star 2, and hit Star 3, go back to Star 2, then continue to Star 3 & so forth.
*hugs all of Siren's former radial cards, twitching slightly*