It's all in perception. I promise that if you're in-game standing on the ground looking at it, it looks massive. It's scaled. Also, if your perception of the ship was influenced by the 1997 movie, the ship in that movie was made to look larger in almost every way. It was not accurate at all. For example, the dock scene where Jack is playing poker...
...shows the ship around 30 feet too high. At this height, the ship would have literally been floating on TOP of the water. Look at this actual photo to see how exaggerated the movie was:
Notice that the line where the black hull meets the white superstructure is below the height of the buildings (passenger sheds). Now, look at the movie still. Yeah, they exaggerated THAT much.
We also get many comments about how small the cabins are. Again, people's perception of the ship and how it should look come from the movie. In reality, the ship and it's rooms were actually rather small. Don't get me wrong. It is "Titanic", but while some people today still believe to to be the "largest ship ever", look at this:
So there. Refresh your perspective and recognize how things really are. She was big for the time, but people today see things differently. Especially when movies skew and stretch the truth.
Edit: Here's a treat and something to strengthen my scale.