this should work. show a full screenshot of your whole Ae interface. highlight the layer in the timeline and press UU so we can see all the modified properties. if you can record the screen as you try to use this tool, show it also.
Are you using a pen or a mouse??
It looks like your layer is scaled way down and the 600px is related to your layer size.
So that is why you see it small. But it is 600px in size.
You should resize your layer to see it bigger or precompose the content you need to apply the liquify.
Does that make sense?
Yes, this was it. Even though I was rescaling my composition size, I wasn't modifying the layer size, and that's why I was seeing no change. Thank you so much!