Some bacteria can survive in air. Mycobacteria, for example, can persist for long periods of time on countertops. However, the bacteria that causes Columnaris is not as hardy.
If the net was dry for several days before you used it again, it should be fine.
Also, the bacteria that causes Columnaris is usually present in most aquatic environments. As long as a fish is healthy, its immune system can generally fight it off. When something happens (stress, age, illness, etc), that's when the bacteria can take hold and overwhelm the fish.
I wouldn't worry about it. The net should be fine by now. BUT if you're still concerned though, you can rinse it in very hot water, then put it outside in the sunshine for a few days. The hot water plus the UV light from the sun will kill just about all bacteria. (Even Mycobacteria can't survive boiling water and sunlight's UV light.)