Can I add pre-mixed coolant to a 70% Water 30% antifreeze mixture?

My car overheated recently, and when I checked it, it looked like it was leaking in the radiator. The overflow reservoir was very low also. I only had a small amount of antifreeze in the boot of the car, so I poured it in and topped it up with water. I'd say there was 70% water and the rest antifreeze. Now, I want to get some coolant back into the car? Should I just top up the reservoir with the coolant and allow the car radiator to take it as it boils away the water or should I do something else?