Source: BBC
CO2 does make .03% of the Earth's atmosphere, now you may have gotten that confused with CO2 percentage of green house gasses in the Earth's atmosphere. Did you know the most potent and prominent greenhouse gas is actually
water vapor in the Earth's atmosphere? It traps more heat than any other gas in the atmosphere and accounts for the vast majority of the greenhouse gasses in the Earth's atmosphere, other things like CO2 and Methane and CFCs are minute in comparison but add to the greenhouse gas. The difference is water vapor is naturally occurring green house gas, gases such as CO2 and methane are not purely contributed by human activity but by a large part, especially after the Industrial Revolution.
The Pie chart below is from the EPA, it shows the percent composition of Green house gases by PEOPLE'S activity, and on that scale CO2 makes up more than 50% of the green house gasses in the atmosphere.
Source: EPA.Gov
So be sure to recognize difference between overall total gases in the Earth's atmosphere from green house gases in the atmosphere.