Noah built it as big as He said it should be. Since He is omnipotent and omniscient, the dimensions He quoted were exactly right. If some animals didn’t fit then their loss was part of His plan. Right? From Genesis:
6:13 And God said unto Noah, The end of all flesh is come before me; for the earth is filled with violence through them; and, behold, I will destroy them with the earth.
6:14 Make thee an ark of gopher wood; rooms shalt thou make in the ark, and shalt pitch it within and without with pitch.
6:15 And this is the fashion which thou shalt make it of: The length of the ark shall be three hundred cubits, the breadth of it fifty cubits, and the height of it thirty cubits.
