I am creating an app in unity and want to augment the 3d models in actual real world scale. When I am project a model (marker less), the projected model seems to be down scaled and doesn't match the real world. Is there any way in which the 3d models that are augmented really match the size of the actual real world object.
The only way to approximate real world scale is to make sure that the DeviceHeightAboveGround is set correctly doing the initialization phase. In the sample application, this is done in with the slider on right side of the screen.
If there is still too much drift in the application:
Consider using object recognition
You could also approximate scale with methods outside of Wikitude.
For instance, if you know two points in the real world of known offset to eachother you could use Wikitude to raycast to both these points. Then divide the Wikitude approximated distance between the two points by the known actual distance to get the scale factor.
Similarly, you could use captured Wikitude camera render textures and query these against a known photogrammetry database to drive world scale.
RTK/ high accuracy GNSS receivers can sometimes be suitable for reading into an Android application, where the global position is used to correct position drift and indirectly correct the scale.