Economy question

Economy question
in year 2009 the GDP of China and USA is roughly 5.0 trillion dollars and 15 trillion dollars respectively
GDP is measuring ONE year gross product,
Then if we calculate THREE years gross product.
Then the GDP of China and USA is 15 trillion dollars and 45 trillion dollars respectively
So the econmy difference between USA and China in the consecutive three years is
45-15=30 trillion dollars?
So taking longer,then the economy difference is bigger?
And even one day,China's GDP = USA's GDP
but the total asset of China is still less than USA,due to China's GDP is less than USA in the previous years.
It is right?