Yes – you can double, triple or even quadruple the recipes.  Mix a bit of the binding powder/water mixture into the paint a little bit at a time so you don’t get a big clump to break apart.  Add a little bit of water until it is smooth enough to paint with. Mix it well.  Some of my mixtures have been thicker than others, but when you use a high quality paint chalk paint brush, it will help you spread it evenly.