It's the ramp up wattage. As you experienced, that first hit was WAY too much for you. You don't need to reach max temperature with your first puff, and you probably don't want to, as you seemed to indicate in your post. Most vapes need a few puffs in order for temperature to be limited. You also don't need to set your mod to "maximum safe temperature" if you don't want to, for example I like a cool vape so I keep my ramp up wattage puny and my temperature settings pretty low.
The reason for choosing a "start up wattage" is that you can start it wherever is comfortable. MTL vapers tend to have lower ramp-up needs and lower temps overall. What temp control will do is under any and all circumstances (within reason) give you an upper limit that you are comfortable with. If you enjoy a cooler vape, then those two parameters can change, sometimes drastically.
Since it takes a bit of time for tanks/coils to heat up, TC gives you the option to choose your "ramp up temperature." How else would the mod know where to start, wattage wise? I mean, if you DIDN'T have the option to select an initial first wattage to start at, your mod would have no place to start. I mean, other than something arbitrary.
You aren't doing anything wrong, nor is your mod probably. It's more a matter of finding out what ramp up and temperature YOU are comfortable with.
Anna