I'm working on something right now that involves mapping out my campus. I'm fairly certain that I've rectified the image correctly, but when I try to measure the distance between two spots, the measuring tool doesn't tell me the correct distance (i.e. it tells me the distance is 0.00226 meters which is not right). I'm also having trouble putting a grid over top of my image (the gridlines just don't appear). I'm using a projected coordinate system instead of a geographic one too, and I'm not sure what I'm doing wrong.
This does sound like a CRS problem. ArcGIS like most other GIS packages can reproject on the fly, so assuming that you have georectified your image correctly, the viewport (project) may be in another CRS that is based on degrees. So make sure the display is in meters and that the measure tool units are also meters (see documentation on changing the units).
However, a common mistake is to assign a CRS rather than actually reproject. Since you have georeferenced the image I am assuming you did this correctly but it is also worth checking. You can do this by checking the coordinates at known locations in the reprojected image to see if they match what you expect. Also check the raster properties to see if the origin is in a sensible place. remember that - while reproject on the fly is great, it is never perfect and sometimes the best option is to reproject your raster to make sure it is in a suitable CRS.
Finally - you don't say how you are trying to put a grid over the image or what you mean by grid. In ESRI-speak 'grid' usually means a raster, but I think you mean a fishnet (see here). If you know the origin of the fishnet in relation to the campus (in real life) then use that and this process will confirm whether your raster is in the right projection.