You need to have a visible disclaimer stating that the opinions expressed on your blog are yours, and not official representation of the Peace Corps (they will give you the official wording of it, but you can rephrase it yourself, if you like.)
You also have to give the blog address to your in-country staff either at staging or when you arrive in-country. You can set the blog to private, and they will never see its contents (only people you approve will see it). Or you can set it to public. They may occasionally flip through it for issues.
I was once asked to remove a post about the problems I had procuring fire spinning fuel for my town festival. The country staff thought someone reading it might think I was a terrorist of some sort, if they did not understand fire spinning. I just set my blog to private until I left peace corps after that.