probably your end function return 5 (5 rows)
but row 5 use _4_(beause rows start with _0_)
you dont need this line to get subfields:
$rows = get_post_meta( 348, 'testimonials', false ); // get all the rows
but what is inside $rows?
if it is the row-count, or you could get it from it.
than use $rows--; after and you have the number you can use for the last row
