I thought your formulas answer was 3.2e+32?? That's a LONG way from 6 Billion.
You stated that 6000 years was too short a period for two people to become 6 billion. The formula of population growth under ideal circumstances proves you are wrong by orders of magnitude. Now you are complaining that there would be too many people in 6000 years. Dance or morn will you.
There are other formulas but also generalize but do take into account that a population will tend to level off as the ability of the environment ceases to be able to sustain growth. There are some others too. Pick any of them and do the math. They all indicate that a population can start at 8 and wind up at 6,000,000,000 in a period of 4300 years.
And you are being obtuse as you often are when someone proves that something you have posted is in error. Now swallow hard and say, "Yep, I was mistaken." like a person of character.