This Bible contradiction is from the Skeptic's Annotated Bible.
No, the gospel is not to be preached to the Gentiles and Samaritans.
Matthew 10:5-6 View context
These twelve Jesus sent forth, and commanded them, saying, Go not into the way of the Gentiles, and into [any] city of the Samaritans enter ye not:
But go rather to the lost sheep of the house of Israel.
Matthew 15:24 View context
But he answered and said, I am not sent but unto the lost sheep of the house of Israel.
Acts 16:6 View context
Now when they had gone throughout Phrygia and the region of Galatia, and were forbidden of the Holy Ghost to preach the word in Asia,
Yes, the gospel is to be preached to everyone, including the Gentiles and Samaritans.
Matthew 28:19 View context
Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
Mark 16:15 View context
And he said unto them, Go ye into all the world, and preach the gospel to every creature.
Acts 8:25 View context
And they, when they had testified and preached the word of the Lord, returned to Jerusalem, and preached the gospel in many villages of the Samaritans.
Acts 15:3 View context
And being brought on their way by the church, they passed through Phenice and Samaria, declaring the conversion of the Gentiles: and they caused great joy unto all the brethren.
Acts 22:21 View context
And he said unto me, Depart: for I will send thee far hence unto the Gentiles.
Acts 28:28 View context
Be it known therefore unto you, that the salvation of God is sent unto the Gentiles, and [that] they will hear it.
Galatians 2:2 View context
And I went up by revelation, and communicated unto them that gospel which I preach among the Gentiles, but privately to them which were of reputation, lest by any means I should run, or had run, in vain.