1- Your sincerity would not be over because your primary intention is to support the charity and work for God. Allah knows this intention, so your sincerity will be kept and Allah will reward you for that. You personally do not want the compensation—you are pressured because of your husband. Allah recognizes that.
2- If you believe this will end up causing tension with your husband, then try to accommodate his request. Talk to the charity and explain to them the situation. Let them know that it’s these circumstances that have compelled you to bring this up. See how they respond. If you found them to hesitate, then perhaps you can just not pursue it. If they were very supportive, then ask them for some compensation.