subscripted assignment dimension mismatch - edge effect

Hello, I am trying to create 92 samples of 5x5 cells from an image. Problem : the loop is stopped by this message : subscripted assignment dimension mismatch. This is due to the edge effect (see below). How can I launch the loop without problem? How can I adapt the matrix size located to the edge?

This is my code :

 for m=1:92
    a(:,:,m) = svf(xy_points(m,1)-2:xy_points(m,1) + 2, xy_points(m,2)-2:xy_points(m,2)+2);
 end

Thanks.