I think you are safe. Just keep an eye on your temp needle. If it climbs too high, shut it down.
There's only one or two brands of coolant you can safely add. Add the wrong thing and you"re in for real expensive trouble because mixing them causes thick goo instead of fluid. Search the forum for threads about coolant and you'll find the correct brands.
BTW, your "heat wave" is what everyone else in the US is now calling "winter"
