Your ruling is correct.
Your ruling is correct. Invisibility states the circumstances that end the condition. Receiving Damage does not end the condition.
Invisibility (PHB 243):
A creature you touch becomes invisible until the spell ends. Anything
the target is wearing or carrying is invisible as long as it is on
the target’s person. The spell ends for a target that attacks or casts
Also see Invisible (PHB 291).
Concentration (PHB 203):
Normal activity, such as moving and attacking, doesn't interfere with
concentration. The following factors can break concentration:
Taking damage. Whenever you take damage while you are concentrating on
a spell, you must make a Constitution saving throw to maintain your
concentration. The DC equals 10 or half the damage you take, whichever
number is higher. If you take damage from multiple sources, such as an
arrow and a dragon's breath, you make a separate saving throw for each
source of damage.
You would have to take damage for damage to interact with your concentration spell. You do not take damage (or activate any of the other triggers that break concentration), so your concentration holds, and you don't have to make a check to maintain your concentration.