I used the same method but of course had different numbers to plug in: 4 gas stations (I am probably forgetting a few in parts of town I didn't frequent) in a town of roughly 10,000 people.

Maybe you'd get a better figure going by number of pumps per person and then <strike>making up</strike> coming up with an average number of pumps per station. For example, (I'm guessing that) the lone gas station in a 200 person down doesn't have a lot of pumps.