that is good. you see that it works 😉
the 8 is because you echo $row_count--;
and testimonials_7_testimonial is the field name for the last row.
now use something like that:
$rows = get_post_meta( 348, 'testimonials', false ); // get number of rows, is inside a array
$row_count = $rows[0]; //get row number out of array
$row_count--; // because first row start with 0 not 1 subtract one from row number
$lastrow_content = 'testimonials_'.$row_count.'_testimonial'; //get last row field
$lastrow_head = 'testimonials_'.$row_count.'_testimonial_header'; //get last row field
$end_testimonial_content = get_post_meta( 348, $lastrow_content, true );// get the last row value
$end_testimonial_header = get_post_meta( 348, $lastrow_head, true ); // get the last row value
$last = '<blockquote>' . $end_testimonial_content . '</blockquote><p>' . $end_testimonial_header . '</p>';
echo $last;
