Adjusting shape of shotcrete pool?

I have a shotcrete pool and spa that is near completion. The problem I have is that an octagonal spa is not exactly octagonal, one side is about 10 inches longer than the shortest when all should be equal. My pool contractor and I agreee that changing two wall by approx 4 inches would fix the problem.
The dilemma is how to add about 2 inches of material to the shotcrete walls without problem of future separation from the original shell.
Any suggestion or advice??

Shotcrete properly applied will not have a bonding problem. Make sure you can extend your jets if on these walls.

Do I have to add additional shotcrete as I'm only adding two inches thickness to a 48inch wall? I was thinking building up some epoxy/concrete compound that can be mixed in small quantities, I assume shotcrete requires pumper truck etc