(Paraphrase) Father, our priest used the wrong readings at Mass on Sunday, using the readings for the Sixth Sunday after Pentecost instead of the Fifth Sunday. Was the Mass valid?
When I read questions like this, I am so greatly saddened by the burden this person has been placed under - the tyranny of being ruled by rules. That receiving the grace of God is not dependent on the promises of God made to us and attached to His Word and Sacraments, but dependent upon the priest doing everything "right," thus making the Mass "valid" or not. And as I said, this person is not alone - there are many questions asked in such a manner, and with such concern and fear.
How grateful I am for the certainty and confidence of the Gospel! That God's forgiveness is not dependent upon me saying exactly the right words in exactly the right way at exactly the right time, but upon Him and His promises, which are sure and true. Luther called such fear the "monster of uncertainty" - how true. But the death and resurrection of Christ leaves no monster or uncertainty. Christ is arisen! Christ is the victor! And so His forgiveness and salvation, given to us in His Word and Sacraments, are true and sure.
Your pastor will make mistakes - count on it! But your Saviour never does. And His gifts are here for you - you can count on it.