Determining nozzle size

Hey everyone,

I'm using a old prusa i3 that I haven't used for a couple years. From memory I think I remember my nozzle size being 0.4 mm. I just made a couple test parts at 100% infill and both sizes of the surfaces look to be quite "groovy" on one part made in PETG and the other part made in PLA is solid on the side made on the bed, but it's top side is groovy or bumpy like the prior part. The next part I want to make at 100 percent solid to have maximum strength and am thinking I should probably try changing the nozzle size in the setting to 0.35 mm and see how the part looks. What do you guys think or what would you do?

The purple part is in PETG and the white is in PLA.