It sounds like you did the best thing you could have done in that situation. Allowing yourself the space to regroup when you feel overwhelmed is a healthy thing. You were able to come back in and go to the concert, so even though the night might have felt like a mess to you, it ended on a successful note. (No pun intended, lol).
Can you bring your family on board to help with the activity scheduling? Even literally - have a white board with a calendar and everyone's appointments. I'm in the same boat as you, having to be the master scheduler. We don't have a large board, but I do write everything on a calendar in the kitchen.
Is there a way that you and your husband could share the traveling? He could take your son to soccer and give you a break one night, then you could take another child another night. It might seem a little less overwhelming if you could split it up somehow, if you're not already.
Again, kudos to you for realizing when you simply couldn't be in the gym, and even more for being able to regroup and come back.