I am attempting to add a scale bar into QGIS Map Composer for a single layer showing a map of Jervis Bay, NSW Australia. I have changed both the project and layer CRS to 'MGA56 (EPSG:28356)' and have tried some other CRS types but the scale is inaccurate. Each time I insert a new scale it shows an area that would be over 3 km long as only 0.2 m or so. I need the scale to be in km and I need it to be an accurate representation of the area I have on the map.
I am completely new to QGIS and have little experience with any of this software.