Hello @inesagsoares
As you are using GCPs, are those placed over all needed images? Do you see some error in position for those GCPs after placing? Before setting the distance, are the GCPs used for the georeferencing of your project?
Regarding your defined distances, what is the proper distance there? As you have quite big differences between defined and calculated distances.
Can you show some print screens of 1Ds view with GCPs and 3D view?