The Gospel of Thomas isn't seen as a Gospel, its 119 "sayings" attributed to Jesus, written in the second century AD, it is not from the Pen of Thomas the Apostle, and is a later forgery, containing many heretical, Gnostic veiws, thoug the text is not 100% Gnostic, it is influenced in that direction.
The fact that it IS a forgery, and the fact that this Pseudographical work contains heretical notions, should be sufficient for anyone to reject it.
All one has to do is read the document to see what it contains, and why it isn't included in the Cannon. "Simon Peter said to them, "Mary should leave us, for females are not worthy of life." Jesus said, "See, I am going to attract her to make her male so that she too might become a living spirit that resembles you males."??? Obviously not the words of Jesus!