print "@data";

This is your problem. Consider this code:

$ perl -E'@a=qw/1 2 3/; print "@a"'
1 2 3
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You wanted to print your lines joined by empty string, but "@array" joins array elements with space (read $" for more info on that). Your original, commented-out approach is better: just read your file by, say, 10 kilobytes and immediately send the data to client:

{
 local $/ = \10240;
 print while <$peunter>;
}
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In this example I tell Perl to read files with diamond operator (<$filehandle>) by 10240 bytes ($/) and loop printing the file pieces until I reach end-of-file.

_{Edit: corrected typo}