Mmm good point on the coolant bottle. I forgot about that one.
There's no reason to not drive it as long as the level is correct. That 750ml of water will make no measurable difference to anything since its diluted the coolant by only a few percent. It might freeze at -29 now instead of -30
Since you have no idea of the concentration that was in there, just add 750ml of neat coolant next time it needs some and you know you've averaged out what you added to be 50:50 ish.