Will this continue to grow and get worse?

Yes.

If that spot on the bottom of a tube I’d just be sanding back the paint (as little as is necessary to get rid of the rust), masking it up and giving it about 4 light coats of sliver gal spray paint from the hardware store.

If it’s in a more obvious spot I would still try the previous method and see how it looks.

If you have to take it to a pro it can get expensive, fast.

Unfortunately. It will get a lot worse.