dont cut it down it will change the chemical composition of it and cause it to shrink more. dont take it right out of the bucket and put it on the wall it needs to be mixed up a bit before use with a paddle and drill to even out the consistancy.. if you want perfect walls its going to take time, patience and several passes to make everything nice and flat otherwise you`ll have to go over it completely with 1/4" drywall or take down the plaster and put up new drywall