So you say, that's an assertion, not a fact.
Let's put the verse in context:
16Jesus said unto her, "Mary!" She turned herself and said unto Him, "Rabboni!" (which is to say, "Master").
17Jesus said unto her, "Touch Me not, for I am not yet ascended to My Father; but go to My brethren and say unto them, `I ascend unto My Father and your Father, and to My God and your God.'"
18Mary Magdalene came and told the disciples that she had seen the Lord, and that He had spoken these things unto her.
19Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in their midst and said unto them, "Peace be unto you."
20And when He had so said, He showed unto them His hands and His side. Then were the disciples glad when they saw the Lord.
21Then said Jesus to them again, "Peace be unto you. As My Father hath sent Me, even so send I you."
22And when He had said this, He breathed on them and said unto them, "Receive ye the Holy Ghost.
23Whosoever sins ye remit, they are remitted unto them; and whosoever sins ye retain, they are retained."
24But Thomas, one of the twelve, called Didymus, was not with them when Jesus came.
25The other disciples therefore said unto him, "We have seen the Lord." But he said unto them, "Unless I shall see in His hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into His side, I will not believe."
26And after eight days the disciples were again within, and Thomas was with them. Then came Jesus, the doors being shut, and stood in their midst and said, "Peace be unto you."
27Then said He to Thomas, "Reach hither thy finger and behold My hands, and reach hither thy hand and thrust it into My side: and be not faithless, but believing."
28And Thomas answered and said unto Him, "My Lord and my God!"
29Jesus said unto him, "Thomas, because thou hast seen Me, thou hast believed. Blessed are they that have not seen and yet have believed."
Note, please Mary did not call Him God.
In Greek and English Lord does not equal GOD in semantic terms. It was a common phrase for a master.
The point of the whole exercise is the third verse in green. Thomas was expressing belief in both Jesus and God by the oath he swore.
I used the 21st century King James for clarity.
Regards,
Scott