Most prefab shower bases have the drain slightly recessed below the concrete floor. This is why a shower rough-in should leave a 12x12 area with no concrete around the drain. This also allows the position of the drain to be moved a bit as needed when the base is installed.
I would cut 12-18" of concrete out around the drain and dig the trap out so it can be moved.
If you are in the USA, I would question the installation further, as a shower drain and any pipe under grade is required to be a minimum of 2" pipe.