Sorry that you had such a rough evening.
Cub scouts are rather young, as I recall from when I was a Brownie. I can imagine your son losing his temper ~ like if he was overly tired & hyper, that's a BIG trigger!
It is very hard in those intense emotional moments to take a step back emotionally & think about the situation rationally instead. But, I do recommend that you always aim towards doing so whenever you feel your emotions building up inside. It isn't easy, but it does become easier the more often it's done. And the tantrums also lose intensity and time!
(((( hugs )))) I have been on that border myself more than a few times, unfortunately. So, I really do understand how you're feeling inside. Try to give yourself a break, let go, and work harder to maintain better control of emotional reactions in the future.