Some times ago, I posted a question that is now -3. I got some good answers that helped me (and I accepted one of them), but the -3 score hints that the question is not good.
Should I delete it?
Assuming you're referring to this, you can't delete it. You can only delete your own questions if they don't have answers. This is the way it works across the entire network - the philosophy is, if it wasn't bad enough to delete before getting answers, the best thing to do is live and learn.