In my experience a 100w non-tube amp isn’t gonna cut the mustard with a full band, particularly if the guitarist is pushing 50+ watts and likes to crank it. If what you are bought was a combo, then yeah, you should take it back and rent a bigger rig. If it’s an amplifier only (head unit, i.e., preamp + power section) and you were using a 100w already, then you are happy with that and ignore this. If there is decent PA, sound reinforcement, then just make sure you have a good DI (with pre, maybe).
Class D is digital switching, right? Such that a chipset manages the amplification, where a class AB is typical big, heavy, copper toroidal transformer?
Class D should be light, and many will handle a 2 ohm load, while traditional amps typically don’t.
When in doubt, listen to @agedhorse!