There are endless ways to cover an ornament. This is one that works well for me. You could use any square cane. This one is a quatrefoil cane. There are lots more intriguing cane tutorials in my etsy shop.
Look at the sides of each cane slice as you add them to the ornament. They should make a straight line from the middle of the bottom to the middle of the top. This is all you have to do to ensure that everything fits.
Some times I very carefully slice off uneven seams. This is a dangerous and unnecessary step, but I thought I'd show you.
Remember, you are in charge of the clay. Squish and stretch it any way you need to to make it fit. Try not to be a perfectionist. I think you'll be happy with the results no matter what. Truly, a little practice goes a long way. Don't expect your first ornament to be a master piece. I think you'll e surprised by how fast you learn if you keep practicing. Each ornament I make gets easier.