To move the whole model:
1. Go to Settings > Program Settings > Building aids and untick the first and second boxes (Collision & 'confine selet to location')
2. Turn off Ortho on the Status Bar (lower right) - that allows you to move in any direction instead of just right angles.
3. On the File menu choose Select All (or Conrtol and A) and everything will highlight.
4. Right Click and choose Move.
You can now drag the whole model anywhere. I found by moving it twice, as close to the centre of the terrain as possible, the zoom issue went.
Finally: Go back to point 1 again and re tick the two boxes (certainly the second one (!) or you will find it very difficult to select the exact thing you want).
In the process of investigating this I have found another issue also unexplained at present but apparently not the cause of the zoom problem.
If you click the Display Framing button, you will notice lines extending to the left and right of the model. These appear to be a corruption in the floor framing. The floor appears as though it was Automatic (was it?) so you have not caused the issue apparently. When I deleted the floor in the lower left room and the passage/ centre room, the line 'extensions' disappeared but reappear if you add floors back into these rooms.
This may cause other problems later so I would suggest you delete all the floors and insert a Floor By Perimeter, or if you want different floor types in differetn rooms, select the floors and on the right click select Replace, and replace the existing floor by one of the Slab (concrete) floors. These do not have framing specified, so seem to work OK. You can change the surface texture to wood or whatever you want for display purposes.
Will keep investigating this further as something is still odd here.
Pat: Yes I noticed and wondered about the size difference too!

Allan