Reviews are posted according to the review date specified within the review form. If that is a date in the past, then it may not show up in “newest reviews.” You can check to see if your review was posted by using the search or by viewing “all reviews” – where they are again sorted by review date, with newest being at the top.
Unfortunately, since the review date is the “publish date” there is no way to make sure reviews with dates in the past are shown with the newest reviews at this time.