Smoothing for 3D Printing

Hi all! So I'm very new to 3D modeling and 3D printing, but learning as I go along.

I'm making pieces to make ceramic molds from. I made the object as I want it in Blender, but when I export the .STL (apply modifiers box checked) and upload to a slicer (Prusa slicer), it shows the object as it was before I smoothed it.

I've made molds from 3D models before in a class and had to sand the piece smooth, but I don't remember there being so much blockiness to the print. Am I not doing something correctly to allow for a smooth print, or do I just need to deal with needing to sand my model if I want a smooth surface?

https://preview.redd.it/dmqyojit7w4g1.png?width=2220&format=png&auto=webp&s=26972cb849abd4bd7e26a130678d63a9c53e1aba