Does the motor turn the same amount in both directions? if so, you are probably rigged correctly and the steering system is what it is.
If the motor turns more one way than the other, you may be able to adjust the steering cable length where it clamps into the holder. It also looks like some adjustment where the steering rod end joins the cable end. It doesn't look like enough adjustment, but who knows.
If that adjustment is not sufficient, I would think you could lengthen the steering rod end a bit. Perhaps a threaded rod plus two bolt couplers would work, if the threads are standard bolt threads. The cable end gets the bolt coupler, the threaded rod screws into that coupler, then another bolt coupler and then the steering rod end. use some blue locktite, and jam nuts as well to keep it all tight.
if the threads on the rod are NPT, some sore of pipe nipple plus 2 couplers might work.
If you cannot do that, some sort of plate or bar extension connected to the steering rod may fix it. It will need two bolts on one end to keep it from swiveling.