If you're not inclined to do it yourself, you can have the car flat-bedded to a shop to have the coolant replaced. That's certainly the safest route. Someone with more knowledge can let you know if it's safe to drive in this way, though I doubt it will be. I would bring it somewhere if you don't want to do the work yourself.
EDIT: I can see some already have let you know the car will be ok to drive to a shop.
We've all had our "limey" moments, so don't kick yourself too badly for it. I broke my convertible top mechanism by putting my lunch bag on top of the roof and forgetting about it being up there when dropping the top a minute later. Simple lapses in judgement that can potentially lead to expensive repairs...they happen.
