Runny cream puff dough happens when you don't cook the dough long enough, or you add too much egg. Make sure to cook the dough after adding the flour until a film forms at the bottom of the saucepan. This can take up to 5 minutes. If you're new to making choux, use a stainless steel pot because the film won't form on a nonstick pot. You may not need to add all the eggs. The eggs are added in 3 additions and you only use as much as you need to get a shiny dough that is the right consistency. The batter should fall off the spoon in a v-shaped ribbon.