I hate to break the news to you, but 600 is too coarse for the clear coat. I painted my cars with single stage which is the same as clear except it has a pigment in it. The coarsest paper I ever used was 1000 and only that coarse if there was some major flaw to remove. Most of the time I used 1500 followed by 2000. If you go over it with 2500 hardly any buffing is required. Be sure and put a few drops of detergent in the water for wet sanding. Change water often. Use a soft sponge and clear water to remove the residue as you sand.
There are some expert finishers on this forum that know far more than I do in regard to finishing model planes as most of my experience has been with cars. Hopefully some of them will jump in here.
Don't make me name names Robert LOL