1 pixel is 0.2 millimeters. 16 pixels for 1 block, is 4.2 millimeters.
I put in 4.2 millimeters times 30,000,000 blocks. That gets you 126,000,000 millimeters.
A minecraft world is not the size of Earth, it's 126 kilometers.
At least, using only pixels.
Where are you getting your pixel size from?
It's commonly thought that a block is 1 meter cubed which would make a pixel 6.25 centimeters or 62 and a half millimeters!
Are you saying that Steve is 7.56 millimeters tall? You can't be serious!
Just because your monitor and Minecraft both use pixels doesn't mean they are the same.
A minecraft block's canon length is 1 meter
Standard MC world if Steve is assumed to be average human size, is 60,000 by 60,000 km, or 3.6 billion sq.kilometers, which is about 7 times larger than Earth surface. (Or 17 times smaller than Jupiter surface)