Don't panic. It will come out of your carpet. Look at it as an opportunity to clean the carpet. Everyone knows carpet always needs cleaned anyway. :)
I alway end up pinning around the edges when I spray baste. I never seem to spray the edges of a big quilt as well as I should. Just a few pins around the border is all I need.
I'm sorry you didn't have a good experience with spray basting. I like it so much better than pinning. It's all I do.