It is actually registering only 1 hemi (screenshot), the last I type in the command:
panarea:/autofs/space/alicudi_002/users/mscat/users/caterina/3T/recons_fsv5.3 $ mri_surf2vol --subject MS089_R01_29 --hemi rh --surfval /autofs/space/alicudi_002/users/mscat/users/valeria/2017_CME_MTR_PET/2017_MTR_PET/GLM0.7/surf2vol/MS089_R01_29/rh.MS089_R01_29.subjspace.mgh
--merge /autofs/space/alicudi_002/users/mscat/users/caterina/3T/recons_fsv5.3/MS089_R01_29/mri/T1.mgz --identity MS089_R01_29 --hemi lh --surfval /autofs/space/alicudi_002/users/mscat/users/valeria/2017_CME_MTR_PET/2017_MTR_PET/GLM0.7/surf2vol/MS089_R01_29/lh.MS089_R01_29.subjspace.mgh
--merge /autofs/space/alicudi_002/users/mscat/users/caterina/3T/recons_fsv5.3/MS089_R01_29/mri/T1.mgz --identity MS089_R01_29 --o /autofs/space/alicudi_002/users/mscat/users/valeria/2017_CME_MTR_PET/2017_MTR_PET/GLM0.7/surf2vol/MS089_R01_29/CME_MS089_R01_29.nii.gz
gdiagno = -1
Using merge volume as template
Using identity matrix for registration
Overriding reg subject MS089_R01_29 with MS089_R01_29
Qa2v: SurfXYZ to VolCRS: ------------------------------
-1.000 0.000 0.000 128.000;
0.000 0.000 -1.000 128.000;
0.000 1.000 0.000 128.000;
0.000 0.000 0.000 1.000;
--------------------------------------------------
subjects dir /autofs/space/alicudi_002/users/mscat/users/caterina/3T/recons_fsv5.3
surface value path /autofs/space/alicudi_002/users/mscat/users/valeria/2017_CME_MTR_PET/2017_MTR_PET/GLM0.7/surf2vol/MS089_R01_29/lh.MS089_R01_29.subjspace.mgh
hemi lh
mksurfmask 0
projfrac 0
outvol path /autofs/space/alicudi_002/users/mscat/users/valeria/2017_CME_MTR_PET/2017_MTR_PET/GLM0.7/surf2vol/MS089_R01_29/CME_MS089_R01_29.nii.gz
template path /autofs/space/alicudi_002/users/mscat/users/caterina/3T/recons_fsv5.3/MS089_R01_29/mri/T1.mgz
------- Anat2Vol Registration (TkReg)----
1.000 0.000 0.000 0.000;
0.000 1.000 0.000 0.000;
0.000 0.000 1.000 0.000;
0.000 0.000 0.000 1.000;
-----------------------------------------
height = 256
width = 256
depth = 256
xsize = 1.000000
ysize = 1.000000
zsize = 1.000000
cdc = -1.000000 0.000000 -0.000000
rdc = 0.000000 -0.000000 -1.000000
sdc = 0.000000 1.000000 -0.000000
xyz0 = 3.587784 22.749557 -8.968880
Gdiag_no -1
Reading surface /autofs/space/alicudi_002/users/mscat/users/caterina/3T/recons_fsv5.3/MS089_R01_29/surf/lh.white
Done reading source surface
INFO: reading /autofs/space/alicudi_002/users/mscat/users/valeria/2017_CME_MTR_PET/2017_MTR_PET/GLM0.7/surf2vol/MS089_R01_29/lh.MS089_R01_29.subjspace.mgh as MGH
Done loading source values (nvtxs = 137036)
INFO: mapping vertices to closest voxel
INFO: resampling surface to volume
INFO: sampled 85686 voxels in the volume
INFO: writing output volume to /autofs/space/alicudi_002/users/mscat/users/valeria/2017_CME_MTR_PET/2017_MTR_PET/GLM0.7/surf2vol/MS089_R01_29/CME_MS089_R01_29.nii.gz