You may want to try a thicker or more rigid cane; that may help. You may also be twisting your wrist slightly during your swing, causing the downward twist/bend. It can take years of practice to line up cane strokes perfectly across both cheeks exactly where you want them and not +/- an inch or two. Janet Hardy has a good book, Canes and Caning, that you might want to check out. You can grab a copy on Amazon.