Power(watts) = Volts X amps.
Your amp limit is 20 for maximum safety with those batteries. And your Voltage is 4.2 ideally but realistically there is a voltage drop in the system so use 3.7.
And with series (pretty much all regulated mods) you add the voltage per battery.
So you're at (3.7v+3.7v)*20a = 148watts
Basically you don't have to worry you could even kick it to 150w and you'd be fine, your mod will handle anything it says it can just fine.
Just as always if you notice something weird with your batteries question it, don't try to continue using them. That should be the only way you have any issues, if something weird happens and you don't take the time to figure out what, why, and fix it.