Remember that old adage/instruction from our elders of pre-Vatican II vintage? They’d always say about your troubles: “Offer it up to make up for what is lacking in the sufferings of Christ.” Or something to that effect.
But the usually unspoken objection is, “What is lacking in the sufferings of Christ that even I could possibly add??”
The answer is the same as it would be if you were outside the Church. “What could I possibly add to the Church?” Or if you were to somehow not make it to Heaven: “What could I possibly add to Heaven of all things??”
The answer is: you! This is what is lacking in the sufferings of Christ. You. We need to enter into the sufferings of our master if we desire to be his disciples. So offer it up for that reason. The suffering will happen regardless. Allow it to be endowed with power by using it as a way to be united to our Lord.