You need to put water in at the 50/50 ratio. Straight antifreeze doesn't have the specific heat capacity that water has, meaning it takes a lot less energy to heat up straight antifreeze than it does water. Your car's metal engine gets very hot because metal takes little energy to heat metal up. Water takes a ton of energy to heat up a little bit, so it draws the heat out as quickly as it builds up when the system works properly. You will risk overheating the motor if you sit for any length of time with just the glycol in the cooling system. It can't remove enough thermal energy to keep the engine cool. 

The only time you want to use straight coolant is if you're using one of the special waterless formulations like Evans. If you've filled your cooling system with 100% regular antifreeze, drain 1/2 of it out and fill back up with distilled water.