Most of the time we just have to live and learn from our mistakes. Happily, that's not the case with blog posts - you can go back into the editor and fix errors in a post even after it's published.
Fixing a post is as easy as finding it and clicking it - you can click anywhere on the body of a post to open it for editing. Make your changes, then click the Update button - voila! Mistakes corrected!
What if you just want to get rid of the entire post? Not a problem - click on the post to open it for editing, then click the arrow next to the update button to delete the post.