You've confused their first and last names. The data is <lname fname score> but you assign those to $fname, $lname, $score

my %hash = ();

while( <DATA> ) {
   my( $lname, $fname, $score ) = split;
   $hash{$lname}{$fname} = $score;
}

#just last names
print join "\n", keys %hash;

print "\n---\n";

#names and scores:
for my $lname ( keys %hash ) {
    for my $fname ( keys %{ $hash{$lname} } ) {
        printf "$lname, $fname:  $hash{$lname}{$fname}\n"
    }
}

__DATA__
Lateur Bart 97
Pierce Jerrad 96
Unknown planetscape 101
Miller Katie 86
[download]

Output:

Pierce
Lateur
Miller
Unknown
---
Pierce, Jerrad:  96
Lateur, Bart:  97
Miller, Katie:  86
Unknown, planetscape:  101
[download]