I'm "happy" to say that your theoretic calculation is wrong... Because the 60 day kuffarah is obliged only once and not for each year.
It is not 38 * 60 = 2280 days
For example; you have broken fasts in the year 2015, 2016 and 2017. The number of the broken days does not matter. Lets consider 10 days in total. So you have to fast in total = 10 + 60 days = 70 days
Or lets say totally 90 days broken in the year 2015-2016-2017 so you have a total of 90 + 60 days = 150 days to fast.