We are all just speculating here but the only "safe answer" is to flush the coolant at once and refill it again. I paid 40$ at the local mechanic to have that done back with my old Saturn. Thats what I would do. Better to spend the forty bucks, assure the safety of your car, and you can get a good night's sleep without the worry of expensive repairs in the future.
Mistakes can happen to anyone, we all make them. But the most important thing is to correct our mistakes immediately as soon as we are aware of them. Good Luck