Nope, you were clear..I misread the measurements...
My guess is that the offset drain will come close, but it won't be enough....may need to chop up some concrete. If you do chop up the concrete plan on making a bigger hole than a smaller hole. You need cut that pipe and keep dirt out. Use 22.5 degree fittings...purchase a street 22.5 degree fitting, too. Dry fit all and see how you make out.
In terms of using a bedding substrate (mortar or structolite) I would tell you to read up on the instructions provided with your shower base. Most manufacturers recommend a bedding substrate to reduce squeeking, but a couple don't. I use structolite whenever possible, even if I have a level floor, as it makes that plastic shower base feel like a custom concrete shower base...real solid!
The bedding substrate can also act to fill in the hole around the pipe once you are lined up correctly.
Keep us posted...O.K?