How to shrink text size

I've come across a strange issue where I can't scale a textbox down to the appropriate size of my game, seeing that font size seems to scale with the world size and not the textbox size. Here's a picture of the issue:

I would like the "RMB" Text to be a fraction of the size it currently is compared to the world size, but I cannot find a way to do so. Any help would be appreciated.