Interpolation based on a condition with AND operator

I am trying to interpolate using some condition. if the diff is less than 2 and diff_cor is less than 20 interpolate else fill with NaNs.

looks like it's not fulfulling my condition, Any suggestion here:

for iii=2:size(data_points)-2
    if diff (iii)<2 && diff_cor(iii)<20
    Data{:,col_num} = interp1(data_points,gamma_cor,new_interpolated_data,'linear');
   
else
  Data{:,col_num}= NaN;
  
    end
end

[KSSV]

YOu first do interpolation with whol epoints...and later introduce NaN's at required indices.