You need to resample the mask so that it is on the gridset as the functional data.
3dresample is one program that can do this for you.
3dresample -master func_task_pp_ICAaroma_bptf.nii.gz -prefix SN_resam.nii -input SN.nii
here the -master dataset is the one you want to match.
3dfractionze can also do this and will give you much more control over process.