Chessie, I always brushed regular white or yellow, undiluted, on my road bed slopes first in say tree foot sections, one side at a time and then went along and sprinkled on the ballast, possibly even carefully pushing into the glue here and there. Then when you have both sides done go back and add the ballast between the ties.
Another way you might try if you want to spread all your ballast at once is to use an eye dropper with your diluted mixture and carefully drop a bit here and there without getting things to wet which it sounds like your doing.
If your using a spray bottle to apply your glue mixture I'd try and use a finer spray is possible and only apply a little bit and let it set up and go back for a second coat.
A base coat of glue on the slopes sure solves a lot of problems though.