This is actually NOT a twist in translation.  The NWT matches all the other translations in this verse. They have no choice because the Greek is crystal clear. (See below)

But what to JWs say about this? Well this is what I’ve heard them say:

“Thomas said “my Lord” …and then he looked up to heaven and said “and my God” giving praise to Jehovah that Jesus is in fact alive. 

Now that’s a lot of explaining and extra words to explain away what Thomas obviously said.