This has happened to a few people and I have yet to find anyone that found a way to remove it ..
Google "Air freshener dash stain"
This damn stain is killing me! I left a vanilla little tree air freshener on my dash and now i have a tree shaped stain on my damn dash. Ive used mcguire wipes and even goo gone and it wont come off. Ive got a 2011 STI. Dash is a hard plastic. Hopefully someone can offer a suggestion before I lose my marbles! Thanks