"%10s" is used to format "!W31801!\t!919!\t!90200809!\t!840!\t!MO!", more than 10 characters, so you might as well have used "%s". You need to apply "%10s" (actually "%-10s" if you want to left-justify) to every field of every line, not just every line.

print('-', (map { sprintf('%-10s', $_) } @header), "\n");
foreach my $line (@data) {
   my @fields = split(/-->/, $line);
   print('-', (map { sprintf('%-10s', $_) } @fields), "\n");
}
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my $format = '-' . ('%-10s' x @header) . "\n";

printf($format, @header);
foreach my $line (@data) {
   printf($format, split(/-->/, $line));
}
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