If you decide that your answer isn't actually useful, deleting it is definitely the right thing to do. I regularly delete answers of mine that I realize are redundant or incorrect.
You'll get any rep you lost from the post back immediately thanks to the recent changes to the system. Previously you would have needed to do a manual rep recalculation.
Posting a lot of answers in areas where you don't know what you're talking about might be frowned upon, though.
Be warned that deleting your answers can be a signal to the spam filter. If you don't have many posts and they've mostly been down-voted, you might actually not want to delete them or you risk being blocked. Once you've got some higher-scoring posts, you could go back and delete them.