I would advise using world painter it's much faster and you can build entire worlds with it. Then you can go in afterwards with voxelsniper, worldedit, and mcedit and iron out all the little details.

ah, good, I'd advise using worldpainter for a base and world edit the rest, but I dont know how you did it, but I would advise creating a size 3 sphere brush of sand or gravel and do /mask air to paste a base, the gravel will fill all holes. Then do a /br cylinder gravel or sand of size 5 and paste it from the top most layer to get a flat base, extend it where you need it then do /br smooth 5, i use 10 but mines got custom sizes, and smooth it out, anyways, good luck again ;)