Your temps of around 215 F. really don't seem out of line for a 100 degree day IMO. Would I keep an eye on it? Absolutely. You always should anyway, but especially on a hot summer day. And I'd try to stay out of boost as much as practical too. But as mentioned above, the stock thermosensor doesn't even trip fans until 108 C. (226 F.).
BTW, while turning the heat on will help a little, it's probably the electrical draw of the heater fan turning on the radiator fans that was doing the most good. Just think, with the FC thermoswitch, you wouldn't have to do that anymore.
