To get this achievement you'll need to fly through 20 stars in a row, not through the middle of them, just keep a combo of 20.
You should be able to get this without any kind of hassle!
I've linked in a video of the first time you get to attempt this achievement, it'll give you an idea of the route you'll be taking and where the stars are!
*Credit to HBPgameguide for the video