Not sure what do you mean by you "calculated it". In your calculation, did you include the 40 percent average mining difficulty every month(per 2017). Meaning every month, bitcoin generated through same hash power is going to reduce. By 12 th month you would almost get nothing mined out(comparing wigh first month). If you are using coinwarz are something similar to calculate, your calculation could be extremly wrong.
Example, when i did a calulation for eth using coin warz, it showed 21 eth will be mined. But when i included 2017's difficulty in calculation, ETH produced is 6 only. The calculation was incorrect by 70 percent.

Also, if the price reaches ATH, difficulty will increase further as a result, lesser coin will be mined.

Either ways, you will end up getting less profit than simply buying bitcoin directly as ur contract will end up producing less bitcoins.