Hi ahmed,
For flat areas a strong imaging geometry is recommended (besides good reference information).
Therefore you should acquire images with a slightly inclined camera instead of nadir ( =pointing straight down). Additionally, add perpendicular tie lines to your survey so that you fly a 'cross hatch' pattern. This will help to improve the error.
And make sure to have sharp and high quality imagery. Motion blur caused by a too high horizontal flight speed will overall increase the error of your 3D reconstruction.
And last but not least, don't forget to run OPTIMISE in Metashape to minimize the reprojection error and improve accuracy.
All the best.
Regards,
SAV