Do your jars have to be upright during the canning process?

Ok, thanks! That's just what I needed to know.

What the rack is doing is elevating the glass off the bottom, keeping the jars from knocking together, and ensuring that there is water flow around each jar. These conditions are all easiest to obtain when the jars are vertical. But you don't necessarily need the rack. I've used canning rings to keep jars off the bottom and a variety of other means, like crumpled foil, to keep the jars separate and allow for water flow. Since you only have one jar, just make sure it's not in direct contact with the bottom, and that it's not going to knock around, banging into the sides of your pot.